GRDB.swift
6.29.3
SQLite数据库的工具包，重点是应用程序开发
自2015年以来自豪地为社区服务
最新版本：2024年10月13日•版本7.0.0-Beta.6•ChangElog•从GRDB 6迁移到GRDB 7
要求：iOS 13.0+ / macOS 10.15+ / tvos 13.0+ / watchos 7.0+•sqlite 3.20.0+•swift 6+ / xcode 16+
接触：
使用此库将应用程序的永久数据保存到SQLite数据库中。它带有可满足共同需求的内置工具：
SQL生成
以持久性和获取方法来增强应用程序模型，以便在不想时不必处理SQL和RAW数据库行。
数据库观察
修改数据库值时获取通知。
强大的并发
多线程应用程序可以有效地使用其数据库，包括支持并发读取和写入的WAL数据库。
迁移
当您运送应用程序的新版本时，可以进化数据库的架构。
利用您的SQLite技能
并非所有开发人员都需要高级SQLite功能。但是当您这样做时，GRDB就会随心所欲。随身携带您的SQL和SQLITE技能，或者随便学习新的技能！
用法•文档•安装•常见问题
import GRDB
// 1. Open a database connection
let dbQueue = try DatabaseQueue ( path : " /path/to/database.sqlite " )
// 2. Define the database schema
try dbQueue . write { db in
try db . create ( table : " player " ) { t in
t . primaryKey ( " id " , . text )
t . column ( " name " , . text ) . notNull ( )
t . column ( " score " , . integer ) . notNull ( )
}
}
// 3. Define a record type
struct Player : Codable , FetchableRecord , PersistableRecord {
var id : String
var name : String
var score : Int
}
// 4. Write and read in the database
try dbQueue . write { db in
try Player ( id : " 1 " , name : " Arthur " , score : 100 ) . insert ( db )
try Player ( id : " 2 " , name : " Barbara " , score : 1000 ) . insert ( db )
}
let players : [ Player ] = try dbQueue . read { db in
try Player . fetchAll ( db )
} try dbQueue . write { db in
try db . execute ( sql : """
CREATE TABLE place (
id INTEGER PRIMARY KEY AUTOINCREMENT,
title TEXT NOT NULL,
favorite BOOLEAN NOT NULL DEFAULT 0,
latitude DOUBLE NOT NULL,
longitude DOUBLE NOT NULL)
""" )
try db . execute ( sql : """
INSERT INTO place (title, favorite, latitude, longitude)
VALUES (?, ?, ?, ?)
""" , arguments : [ " Paris " , true , 48.85341 , 2.3488 ] )
let parisId = db . lastInsertedRowID
// Avoid SQL injection with SQL interpolation
try db . execute ( literal : """
INSERT INTO place (title, favorite, latitude, longitude)
VALUES ( ( " King's Cross " ) , ( true ) , ( 51.52151 ) , ( - 0.12763 ) )
""" )
}请参阅执行更新
try dbQueue . read { db in
// Fetch database rows
let rows = try Row . fetchCursor ( db , sql : " SELECT * FROM place " )
while let row = try rows . next ( ) {
let title : String = row [ " title " ]
let isFavorite : Bool = row [ " favorite " ]
let coordinate = CLLocationCoordinate2D (
latitude : row [ " latitude " ] ,
longitude : row [ " longitude " ] )
}
// Fetch values
let placeCount = try Int . fetchOne ( db , sql : " SELECT COUNT(*) FROM place " ) ! // Int
let placeTitles = try String . fetchAll ( db , sql : " SELECT title FROM place " ) // [String]
}
let placeCount = try dbQueue . read { db in
try Int . fetchOne ( db , sql : " SELECT COUNT(*) FROM place " ) !
}请参阅提取查询
struct Place {
var id : Int64 ?
var title : String
var isFavorite : Bool
var coordinate : CLLocationCoordinate2D
}
// snip: turn Place into a "record" by adopting the protocols that
// provide fetching and persistence methods.
try dbQueue . write { db in
// Create database table
try db . create ( table : " place " ) { t in
t . autoIncrementedPrimaryKey ( " id " )
t . column ( " title " , . text ) . notNull ( )
t . column ( " favorite " , . boolean ) . notNull ( ) . defaults ( to : false )
t . column ( " longitude " , . double ) . notNull ( )
t . column ( " latitude " , . double ) . notNull ( )
}
var berlin = Place (
id : nil ,
title : " Berlin " ,
isFavorite : false ,
coordinate : CLLocationCoordinate2D ( latitude : 52.52437 , longitude : 13.41053 ) )
try berlin . insert ( db )
berlin . id // some value
berlin . isFavorite = true
try berlin . update ( db )
}请参阅记录
try dbQueue . read { db in
// Place
let paris = try Place . find ( db , id : 1 )
// Place?
let berlin = try Place . filter ( Column ( " title " ) == " Berlin " ) . fetchOne ( db )
// [Place]
let favoritePlaces = try Place
. filter ( Column ( " favorite " ) == true )
. order ( Column ( " title " ) )
. fetchAll ( db )
// Int
let favoriteCount = try Place . filter ( Column ( " favorite " ) ) . fetchCount ( db )
// SQL is always welcome
let places = try Place . fetchAll ( db , sql : " SELECT * FROM place " )
}查看界面
// Define the observed value
let observation = ValueObservation . tracking { db in
try Place . fetchAll ( db )
}
// Start observation
let cancellable = observation . start (
in : dbQueue ,
onError : { error in ... } ,
onChange : { ( places : [ Place ] ) in print ( " Fresh places: ( places ) " ) } )对联合收割机和rxswift的现成支持：
// Combine
let cancellable = observation . publisher ( in : dbQueue ) . sink (
receiveCompletion : { completion in ... } ,
receiveValue : { ( places : [ Place ] ) in print ( " Fresh places: ( places ) " ) } )
// RxSwift
let disposable = observation . rx . observe ( in : dbQueue ) . subscribe (
onNext : { ( places : [ Place ] ) in print ( " Fresh places: ( places ) " ) } ,
onError : { error in ... } )请参阅数据库观察，组合支持，RXGRDB。
GRDB在SQLite的顶部运行：您应该熟悉SQLITE常见问题。有关一般和详细信息，请跳到SQLite文档。
常问问题
示例代码
下面的安装步骤具有GRDB使用目标操作系统发货的SQLite版本。
有关使用SQLCIPHER的GRDB安装过程，请参见加密。
请参阅具有SQLite的自定义构建的GRDB安装过程的自定义SQLITE构建。
Swift软件包管理器可自动化Swift代码的分布。要将GRDB与SPM一起使用，请添加依赖项到https://github.com/groue/GRDB.swift.git
GRDB提供了两个库， GRDB和GRDB-dynamic 。只选择一个。如有疑问，更喜欢GRDB 。如果您要将其与应用程序中的多个目标链接，并且只希望链接到共享的，动态的框架一次， GRDB-dynamic库可以揭示有用。有关更多信息，请参阅如何将Swift软件包链接为动态。
注意：当前不支持Linux。
CocoApods是Xcode项目的依赖项经理。要将GRDB与Cocoapods（1.2版或更高版本）一起使用，请在您的Podfile中指定：
pod 'GRDB.swift'GRDB可以作为框架或静态库安装。
Cocoapods安装的重要说明
由于Cocoapods中的问题，目前无法将新版本的GRDB部署到可可录。 Cocoapods上的最后一个版本是6.24.1。要使用Cocoapods安装以后版本的GRDB，请使用以下解决方法之一：
取决于GRDB6分支。如果Cocoapods接受新的GRDB版本，这或多或少与pod 'GRDB.swift', '~> 6.0'通常这样做：
# Can't use semantic versioning due to https://github.com/CocoaPods/CocoaPods/issues/11839
pod 'GRDB.swift' , git : 'https://github.com/groue/GRDB.swift.git' , branch : 'GRDB6'明确取决于特定版本（用您要使用的版本替换标签）：
# Can't use semantic versioning due to https://github.com/CocoaPods/CocoaPods/issues/11839
# Replace the tag with the tag that you want to use.
pod 'GRDB.swift' , git : 'https://github.com/groue/GRDB.swift.git' , tag : 'v6.29.0' 迦太基不受支持。有关此决定的某些背景，请参见＃433。
下载GRDB的副本，或克隆其存储库，并确保您查看最新标记的版本。
将GRDB.xcodeproj项目嵌入您自己的项目中。
在应用程序目标的“构建阶段”选项卡（WatchOS的扩展目标）的“构建阶段”选项卡的目标依赖项部分中添加GRDB目标。
将GRDB.framework添加到应用程序目标一般选项卡的嵌入式二进制组（WatchOS的扩展目标）。
GRDB提供了两个用于访问SQLITE数据库的类： DatabaseQueue和DatabasePool ：
import GRDB
// Pick one:
let dbQueue = try DatabaseQueue ( path : " /path/to/database.sqlite " )
let dbPool = try DatabasePool ( path : " /path/to/database.sqlite " )差异是：
如果不确定，请选择DatabaseQueue 。稍后，您将始终能够切换到DatabasePool 。
有关打开连接时的更多信息和提示，请参见数据库连接。
在文档的这一部分中，我们将讨论SQL。如果SQL不是您的茶，请跳到查询界面。
DatabaseValueConvertible ：自定义值类型的协议高级主题：
授予数据库连接后， execute(sql:arguments:)方法将执行不返回任何数据库行的SQL语句，例如CREATE TABLE ，Insert， INSERT ， DELETE ， ALTER ，Ett。
例如：
try dbQueue . write { db in
try db . execute ( sql : """
CREATE TABLE player (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL,
score INT)
""" )
try db . execute (
sql : " INSERT INTO player (name, score) VALUES (?, ?) " ,
arguments : [ " Barbara " , 1000 ] )
try db . execute (
sql : " UPDATE player SET score = :score WHERE id = :id " ,
arguments : [ " score " : 1000 , " id " : 1 ] )
}
}这?和符合结合的键，例如:score是语句参数。如上所述，您可以通过数组或字典进行参数。有关支持的参数类型（BOOL，INT，String，Date，Swift Enums等）的更多信息，请参见值，以及有关SQLITE参数详细文档的StatementArguments 。
您还可以将查询参数嵌入到SQL查询中，并使用execute(literal:) ，如下示例。有关更多详细信息，请参见SQL插值。
try dbQueue . write { db in
let name = " O'Brien "
let score = 550
try db . execute ( literal : """
INSERT INTO player (name, score) VALUES ( ( name ) , ( score ) )
""" )
}永远不要将值直接嵌入您的原始SQL字符串中。有关更多信息，请参见避免SQL注入：
// WRONG: don't embed values in raw SQL strings
let id = 123
let name = textField . text
try db . execute (
sql : " UPDATE player SET name = ' ( name ) ' WHERE id = ( id ) " )
// CORRECT: use arguments dictionary
try db . execute (
sql : " UPDATE player SET name = :name WHERE id = :id " ,
arguments : [ " name " : name , " id " : id ] )
// CORRECT: use arguments array
try db . execute (
sql : " UPDATE player SET name = ? WHERE id = ? " ,
arguments : [ name , id ] )
// CORRECT: use SQL Interpolation
try db . execute (
literal : " UPDATE player SET name = ( name ) WHERE id = ( id ) " )加入多个陈述，与半隆：
try db . execute ( sql : """
INSERT INTO player (name, score) VALUES (?, ?);
INSERT INTO player (name, score) VALUES (?, ?);
""" , arguments : [ " Arthur " , 750 , " Barbara " , 1000 ] )
try db . execute ( literal : """
INSERT INTO player (name, score) VALUES ( ( " Arthur " ) , ( 750 ) );
INSERT INTO player (name, score) VALUES ( ( " Barbara " ) , ( 1000 ) );
""" )当您要确保执行单个语句时，请使用准备好的Statement 。
在插入语句之后，您可以使用lastInsertedRowID获取插入行的行ID：
try db . execute (
sql : " INSERT INTO player (name, score) VALUES (?, ?) " ,
arguments : [ " Arthur " , 1000 ] )
let playerId = db . lastInsertedRowID不要错过提供经典持久方法的记录：
var player = Player ( name : " Arthur " , score : 1000 )
try player . insert ( db )
let playerId = player . id数据库连接可让您获取数据库行，纯值和自定义模型也称为“记录”。
行是SQL查询的原始结果：
try dbQueue . read { db in
if let row = try Row . fetchOne ( db , sql : " SELECT * FROM wine WHERE id = ? " , arguments : [ 1 ] ) {
let name : String = row [ " name " ]
let color : Color = row [ " color " ]
print ( name , color )
}
}值是Bool，Int，String，Date，Swift Enums等。存储在行列中：
try dbQueue . read { db in
let urls = try URL . fetchCursor ( db , sql : " SELECT url FROM wine " )
while let url = try urls . next ( ) {
print ( url )
}
}记录是您的应用程序对象，可以从行初始化自己：
let wines = try dbQueue . read { db in
try Wine . fetchAll ( db , sql : " SELECT * FROM wine " )
}在整个GRDB中，您始终可以获取任何可获得类型（数据库行，简单值或自定义记录）的光标，数组，集合或单个值：
try Row . fetchCursor ( ... ) // A Cursor of Row
try Row . fetchAll ( ... ) // [Row]
try Row . fetchSet ( ... ) // Set<Row>
try Row . fetchOne ( ... ) // Row? fetchCursor返回一个光标，超过获取的值：
let rows = try Row . fetchCursor ( db , sql : " SELECT ... " ) // A Cursor of Row fetchAll返回一个数组：
let players = try Player . fetchAll ( db , sql : " SELECT ... " ) // [Player] fetchSet返回一组：
let names = try String . fetchSet ( db , sql : " SELECT ... " ) // Set<String> fetchOne返回一个可选值，并消耗单个数据库行（如果有）。
let count = try Int . fetchOne ( db , sql : " SELECT COUNT(*) ... " ) // Int?所有这些获取方法都需要一个包含单个SQL语句的SQL字符串。当您想从多个语句与半隆一起获取时，请迭代SQL字符串中的多个准备好的语句。
Cursor
每当您从数据库中消耗几行时，都可以获取数组，集合或光标。
fetchAll()和fetchSet()方法返回常规的swift数组和集合，您像所有其他数组和集合一样迭代：
try dbQueue . read { db in
// [Player]
let players = try Player . fetchAll ( db , sql : " SELECT ... " )
for player in players {
// use player
}
}与数组和集合不同， fetchCursor()返回的光标逐步加载其结果：
try dbQueue . read { db in
// Cursor of Player
let players = try Player . fetchCursor ( db , sql : " SELECT ... " )
while let player = try players . next ( ) {
// use player
}
}光标无法在任何线程上使用：您必须在创建的调度队列上消耗光标。特别是，不要从数据库访问方法中提取光标：
// Wrong
let cursor = try dbQueue . read { db in
try Player . fetchCursor ( db , ... )
}
while let player = try cursor . next ( ) { ... }相反，任何线程都可以消耗数组和集合：
// OK
let array = try dbQueue . read { db in
try Player . fetchAll ( db , ... )
}
for player in array { ... }光标只能迭代一次。阵列和集合可以迭代多次。
依从者迭代数据库会以懒惰的方式产生，并且不会消耗太多记忆。数组和集合包含数据库值的副本，当有很多提取结果时，可能会需要大量内存。
光标是可以直接访问SQLite的，与数组和集合不同，这些数组和集合必须花时间复制数据库值。如果您照顾额外的性能，则可能更喜欢光标。
光标可以提供快速收藏。
当您想要阵列或集合时，大多数时候都会使用fetchAll或fetchSet 。对于更具体的需求，您可能更喜欢以下初始化器之一。他们所有人都接受一个额外的可选minimumCapacity参数，该参数有助于当您了解光标中的元素数量时（内置的fetchAll和fetchSet不会执行此类优化）。
数组和所有类型符合RangeReplaceableCollection ：
// [String]
let cursor = try String . fetchCursor ( db , ... )
let array = try Array ( cursor )套：
// Set<Int>
let cursor = try Int . fetchCursor ( db , ... )
let set = try Set ( cursor )字典：
// [Int64: [Player]]
let cursor = try Player . fetchCursor ( db )
let dictionary = try Dictionary ( grouping : cursor , by : { $0 . teamID } )
// [Int64: Player]
let cursor = try Player . fetchCursor ( db ) . map { ( $0 . id , $0 ) }
let dictionary = try Dictionary ( uniqueKeysWithValues : cursor )光标采用光标协议，看起来很像Swift的标准懒惰序列。因此，光标具有许多便利的方法： compactMap ， contains ， dropFirst ， dropLast ，drop， drop(while:) ， enumerated ， filter ， first ，first， flatMap ，flatmap， forEach ，foreach， joined ， joined(separator:) ， max ， max(by:) min ， min(by:) ， map ， prefix ， prefix(while:) ， reduce ， reduce(into:) ， suffix ：
// Prints all Github links
try URL
. fetchCursor ( db , sql : " SELECT url FROM link " )
. filter { url in url . host == " github.com " }
. forEach { url in print ( url ) }
// An efficient cursor of coordinates:
let locations = try Row .
. fetchCursor ( db , sql : " SELECT latitude, longitude FROM place " )
. map { row in
CLLocationCoordinate2D ( latitude : row [ 0 ] , longitude : row [ 1 ] )
}光标不是快速序列。这是因为Swift序列无法处理迭代错误，当阅读SQLite结果可能随时失败。
光标需要一点谨慎：
不要在光标迭代期间修改结果：
// Undefined behavior
while let player = try players . next ( ) {
try db . execute ( sql : " DELETE ... " )
}不要将Row的光标变成数组或集合。您不会得到您期望的不同行。要获取一排行，请使用Row.fetchAll(...) 。要获取一组行，请使用Row.fetchSet(...) 。一般而言，请确保每当从光标中提取它时，请确保复制行以供以后使用： row.copy() 。
如果您看不到或不关心差异，请使用阵列。如果您关心内存和性能，请在适当时使用光标。
Row提取行，阵列，集或单行的光标（请参阅获取方法）：
try dbQueue . read { db in
try Row . fetchCursor ( db , sql : " SELECT ... " , arguments : ... ) // A Cursor of Row
try Row . fetchAll ( db , sql : " SELECT ... " , arguments : ... ) // [Row]
try Row . fetchSet ( db , sql : " SELECT ... " , arguments : ... ) // Set<Row>
try Row . fetchOne ( db , sql : " SELECT ... " , arguments : ... ) // Row?
let rows = try Row . fetchCursor ( db , sql : " SELECT * FROM wine " )
while let row = try rows . next ( ) {
let name : String = row [ " name " ]
let color : Color = row [ " color " ]
print ( name , color )
}
}
let rows = try dbQueue . read { db in
try Row . fetchAll ( db , sql : " SELECT * FROM player " )
}论点是填充位置的可选阵列或词典?和结肠固定的钥匙，例如:name ：
let rows = try Row . fetchAll ( db ,
sql : " SELECT * FROM player WHERE name = ? " ,
arguments : [ " Arthur " ] )
let rows = try Row . fetchAll ( db ,
sql : " SELECT * FROM player WHERE name = :name " ,
arguments : [ " name " : " Arthur " ] )有关支持的参数类型（BOOL，INT，String，Date，Swift Enums等）的更多信息，请参见值，以及有关SQLITE参数详细文档的StatementArguments 。
与包含数据库行副本的行阵列不同，行光标靠近SQLite金属，并且需要一点护理：
注意：不要将
Row的光标变成数组或集合。您不会得到您期望的不同行。要获取一排行，请使用Row.fetchAll(...)。要获取一组行，请使用Row.fetchSet(...)。一般而言，请确保每当从光标中提取它时，请确保复制行以供以后使用：row.copy()。
通过索引或列名读取列值：
let name : String = row [ 0 ] // 0 is the leftmost column
let name : String = row [ " name " ] // Leftmost matching column - lookup is case-insensitive
let name : String = row [ Column ( " name " ) ] // Using query interface's Column确保在值可能为null时要求可选：
let name : String ? = row [ " name " ] row[]下标返回您要求的类型。有关支持的价值类型的更多信息，请参见值：
let bookCount : Int = row [ " bookCount " ]
let bookCount64 : Int64 = row [ " bookCount " ]
let hasBooks : Bool = row [ " bookCount " ] // false when 0
let string : String = row [ " date " ] // "2015-09-11 18:14:15.123"
let date : Date = row [ " date " ] // Date
self . date = row [ " date " ] // Depends on the type of the property.您也可以使用as类型铸造操作员：
row [ ... ] as Int
row [ ... ] as Int ?警告：避免使用
as!和as?操作员：if let int = row [ ... ] as? Int { ... } // BAD - doesn't work if let int = row [ ... ] as Int ? { ... } // GOOD
警告：避免使用尼尔粉化的行值，而更喜欢
coalesce方法：let name : String ? = row [ " nickname " ] ?? row [ " name " ] // BAD - doesn't work let name : String ? = row . coalesce ( [ " nickname " , " name " ] ) // GOOD
一般而言，您可以提取所需的类型，只要可以从基础sqlite值转换：
成功的转换包括：
有关支持类型的更多信息，请参见值（Bool，INT，String，Date，Swift Enums等）。
零返回零。
let row = try Row . fetchOne ( db , sql : " SELECT NULL " ) !
row [ 0 ] as Int ? // nil
row [ 0 ] as Int // fatal error: could not convert NULL to Int.但是，有一个例外：数据库值类型：
row [ 0 ] as DatabaseValue // DatabaseValue.null缺少列返回无。
let row = try Row . fetchOne ( db , sql : " SELECT 'foo' AS foo " ) !
row [ " missing " ] as String ? // nil
row [ " missing " ] as String // fatal error: no such column: missing您可以使用hasColumn方法明确检查列存在。
无效的转换造成了致命错误。
let row = try Row . fetchOne ( db , sql : " SELECT 'Mom’s birthday' " ) !
row [ 0 ] as String // "Mom’s birthday"
row [ 0 ] as Date ? // fatal error: could not convert "Mom’s birthday" to Date.
row [ 0 ] as Date // fatal error: could not convert "Mom’s birthday" to Date.
let row = try Row . fetchOne ( db , sql : " SELECT 256 " ) !
row [ 0 ] as Int // 256
row [ 0 ] as UInt8 ? // fatal error: could not convert 256 to UInt8.
row [ 0 ] as UInt8 // fatal error: could not convert 256 to UInt8.这些转换性致命错误可以通过数据库值类型避免：
let row = try Row . fetchOne ( db , sql : " SELECT 'Mom’s birthday' " ) !
let dbValue : DatabaseValue = row [ 0 ]
if dbValue . isNull {
// Handle NULL
} else if let date = Date . fromDatabaseValue ( dbValue ) {
// Handle valid date
} else {
// Handle invalid date
}这种额外的详细性是必须处理不信任数据库的结果：您可以考虑修复数据库的内容。有关更多信息，请参见致命错误。
SQLite具有弱类型系统，并提供便利转换，可以将字符串变成int，double to Blob，等等。
GRDB有时会让这些转换进行：
let rows = try Row . fetchCursor ( db , sql : " SELECT '20 small cigars' " )
while let row = try rows . next ( ) {
row [ 0 ] as Int // 20
}不要吓到：这些转换并不能阻止SQLite成为您想要使用的非常成功的数据库引擎。 GRDB添加了上面描述的安全检查。您还可以使用数据库值类型完全防止这些便利转换。
DatabaseValue
DatabaseValue是SQLite和您的值之间的中间类型，它提供了有关数据库中存储的原始值的信息。
就像其他值类型一样，您可以获得DatabaseValue ：
let dbValue : DatabaseValue = row [ 0 ]
let dbValue : DatabaseValue ? = row [ " name " ] // nil if and only if column does not exist
// Check for NULL:
dbValue . isNull // Bool
// The stored value:
dbValue . storage . value // Int64, Double, String, Data, or nil
// All the five storage classes supported by SQLite:
switch dbValue . storage {
case . null : print ( " NULL " )
case . int64 ( let int64 ) : print ( " Int64: ( int64 ) " )
case . double ( let double ) : print ( " Double: ( double ) " )
case . string ( let string ) : print ( " String: ( string ) " )
case . blob ( let data ) : print ( " Data: ( data ) " )
}您可以从DatabaseValue中提取常规值（Bool，Int，String，Date，Swift Enums等），并使用FromDatabaseValue（）方法：
let dbValue : DatabaseValue = row [ " bookCount " ]
let bookCount = Int . fromDatabaseValue ( dbValue ) // Int?
let bookCount64 = Int64 . fromDatabaseValue ( dbValue ) // Int64?
let hasBooks = Bool . fromDatabaseValue ( dbValue ) // Bool?, false when 0
let dbValue : DatabaseValue = row [ " date " ]
let string = String . fromDatabaseValue ( dbValue ) // "2015-09-11 18:14:15.123"
let date = Date . fromDatabaseValue ( dbValue ) // Date? fromDatabaseValue返回无效转换的零：
let row = try Row . fetchOne ( db , sql : " SELECT 'Mom’s birthday' " ) !
let dbValue : DatabaseValue = row [ 0 ]
let string = String . fromDatabaseValue ( dbValue ) // "Mom’s birthday"
let int = Int . fromDatabaseValue ( dbValue ) // nil
let date = Date . fromDatabaseValue ( dbValue ) // nil 行采用标准的随机计算协议，可以看作是数据库值的字典：
// All the (columnName, dbValue) tuples, from left to right:
for (columnName , dbValue ) in row {
...
}您可以从字典（标准的Swift词典和Nsdictionary）构建行。有关支持类型的更多信息，请参见值：
let row : Row = [ " name " : " foo " , " date " : nil ]
let row = Row ( [ " name " : " foo " , " date " : nil ] )
let row = Row ( /* [AnyHashable: Any] */ ) // nil if invalid dictionary但是行不是真实的词典：它们可能包含重复的列：
let row = try Row . fetchOne ( db , sql : " SELECT 1 AS foo, 2 AS foo " ) !
row . columnNames // ["foo", "foo"]
row . databaseValues // [1, 2]
row [ " foo " ] // 1 (leftmost matching column)
for (columnName , dbValue ) in row { ... } // ("foo", 1), ("foo", 2)当您从一排构建字典时，您必须放弃相同的列，并选择如何显示数据库值。例如：
一个[String: DatabaseValue]字典，该字典在重复列名的情况下保持最左值：
let dict = Dictionary ( row , uniquingKeysWith : { ( left , _ ) in left } )一个[String: AnyObject]字典在重复列名的情况下保持最右边的值。该词典与FMDB的FMResultset结果与fmdb相同。它包含null列的NSNULL值，可以与Objective-C共享：
let dict = Dictionary (
row . map { ( column , dbValue ) in
( column , dbValue . storage . value as AnyObject )
} ,
uniquingKeysWith : { ( _ , right ) in right } ) [String: Any]可以馈送的字典，例如jsonserialization：
let dict = Dictionary (
row . map { ( column , dbValue ) in
( column , dbValue . storage . value )
} ,
uniquingKeysWith : { ( left , _ ) in left } )有关更多信息，请参见Dictionary.init(_:uniquingKeysWith:)的文档。
DatabaseValueConvertible
您可以直接获取值，而不是行。有许多支持的价值类型（Bool，INT，String，Date，Swift Enums等）。
像行一样，以光标，数组，集合或单个值的形式获取值（请参阅获取方法）。值是从SQL查询的最左列提取的：
try dbQueue . read { db in
try Int . fetchCursor ( db , sql : " SELECT ... " , arguments : ... ) // A Cursor of Int
try Int . fetchAll ( db , sql : " SELECT ... " , arguments : ... ) // [Int]
try Int . fetchSet ( db , sql : " SELECT ... " , arguments : ... ) // Set<Int>
try Int . fetchOne ( db , sql : " SELECT ... " , arguments : ... ) // Int?
let maxScore = try Int . fetchOne ( db , sql : " SELECT MAX(score) FROM player " ) // Int?
let names = try String . fetchAll ( db , sql : " SELECT name FROM player " ) // [String]
} Int.fetchOne在两种情况下返回零：选择语句没有产生行，或一个带有空值的行：
// No row:
try Int . fetchOne ( db , sql : " SELECT 42 WHERE FALSE " ) // nil
// One row with a NULL value:
try Int . fetchOne ( db , sql : " SELECT NULL " ) // nil
// One row with a non-NULL value:
try Int . fetchOne ( db , sql : " SELECT 42 " ) // 42对于可能包含null的请求，提取选项：
try dbQueue . read { db in
try Optional < Int > . fetchCursor ( db , sql : " SELECT ... " , arguments : ... ) // A Cursor of Int?
try Optional < Int > . fetchAll ( db , sql : " SELECT ... " , arguments : ... ) // [Int?]
try Optional < Int > . fetchSet ( db , sql : " SELECT ... " , arguments : ... ) // Set<Int?>
}提示：当您获取一个值时，一个高级用例是为了区分没有行的陈述的案例，或一个带有空值的行。为此，请使用
Optional<Int>.fetchOne，返回双可选Int??：// No row: try Optional < Int > . fetchOne ( db , sql : " SELECT 42 WHERE FALSE " ) // .none // One row with a NULL value: try Optional < Int > . fetchOne ( db , sql : " SELECT NULL " ) // .some(.none) // One row with a non-NULL value: try Optional < Int > . fetchOne ( db , sql : " SELECT 42 " ) // .some(.some(42))
有许多支持的价值类型（Bool，INT，String，Date，Swift Enums等）。有关更多信息，请参见值。
GRDB船只对以下值类型进行内置支持：
Swift Standard库：Bool，Double，Float，所有签名和未签名的整数类型，字符串，Swift Enums。
基础：数据，日期，dateComponents，Decimal，nsnull，nsnumber，nsstring，url，uuid。
CoreGraphics ：CGFLOAT。
DatabaseValue ，该类型提供了有关数据库中存储的原始值的信息。
全文图案：FTS3PATTERN和FTS5PATTERN。
一般而言，所有采用DatabaseValueConvertible valueconvertible协议的类型。
值可以用作语句参数：
let url : URL = ...
let verified : Bool = ...
try db . execute (
sql : " INSERT INTO link (url, verified) VALUES (?, ?) " ,
arguments : [ url , verified ] )值可以从行中提取：
let rows = try Row . fetchCursor ( db , sql : " SELECT * FROM link " )
while let row = try rows . next ( ) {
let url : URL = row [ " url " ]
let verified : Bool = row [ " verified " ]
}值可以直接获取：
let urls = try URL . fetchAll ( db , sql : " SELECT url FROM link " ) // [URL]在记录中使用值：
struct Link : FetchableRecord {
var url : URL
var isVerified : Bool
init ( row : Row ) {
url = row [ " url " ]
isVerified = row [ " verified " ]
}
}在查询接口中使用值：
let url : URL = ...
let link = try Link . filter ( Column ( " url " ) == url ) . fetchOne ( db )数据适合Blob Sqlite列。它可以像其他值一样从数据库中存储和获取：
let rows = try Row . fetchCursor ( db , sql : " SELECT data, ... " )
while let row = try rows . next ( ) {
let data : Data = row [ " data " ]
}在请求迭代的每个步骤中， row[]下标创建了数据库字节的两个副本：一个由sqlite获取的副本，而另一个则存储在Swift数据值中。
您有机会通过不复制SQLite获取的数据来节省内存：
while let row = try rows . next ( ) {
try row . withUnsafeData ( name : " data " ) { ( data : Data ? ) in
...
}
}非被关注的数据的寿命不超过迭代步骤：确保您不会超过此一点。
可以从数据库中存储和获取日期和数据组件。
这是GRDB如何支持SQLITE支持的各种日期格式：
| sqlite格式 | 日期 | DateComponents |
|---|---|---|
| yyyy-mm-dd | 阅读� | 读 /写 |
| YYYY-MM-DD HH：MM | 阅读 | 阅读² /写 |
| Yyyy-MM-DD HH：MM：SS | 阅读 | 阅读² /写 |
| Yyyy-MM-DD HH：MM：SS.SSS | 阅读¹² /写 | 阅读² /写 |
| YYYY-MM-DD T HH：MM | 阅读 | 阅读² |
| Yyyy-MM-DD T HH：MM：SS | 阅读 | 阅读² |
| Yyyy-MM-DD T HH：MM：SS.SSS | 阅读 | 阅读² |
| HH：MM | 阅读² /写 | |
| HH：MM：SS | 阅读² /写 | |
| HH：MM：SS.SSS | 阅读² /写 | |
| 自Unix时期以来的时间戳 | 阅读³ | |
now |
β缺少的组件被认为为零。日期存储并在UTC时区读取，除非格式之后是时区指示器⁽²⁾。
²该格式可以选择后面是[+-]HH:MM或Z形式的时区指示器。
³GRDB2+将数值解释为燃料Date(timeIntervalSince1970:) 。以前的GRDB版本用来将数字解释为朱利安时代。朱利安的日子仍然得到支持， Date(julianDay:) initializer。
警告：SQLite日期格式的有效年份范围为0000-9999。当您的应用程序需要在此范围之外处理数年时，您将需要选择其他日期格式。请参阅以下章节。
就像其他值一样，可以从数据库中存储和获取日期：
try db . execute (
sql : " INSERT INTO player (creationDate, ...) VALUES (?, ...) " ,
arguments : [ Date ( ) , ... ] )
let row = try Row . fetchOne ( db , ... ) !
let creationDate : Date = row [ " creationDate " ]使用格式“ Yyyy-MM-DD HH：MM：SS.SSS”中的格式存储日期。这是毫秒的精确度。
注意：选择此格式是因为它是唯一的格式：
- 可比较（
ORDER BY date）- 可与sqlite关键字current_timestamp（
WHERE date > CURRENT_TIMESTAMP工作）可比- 能够喂养sqlite日期和时间功能
- 足够精确
警告：SQLite日期格式的有效年份范围为0000-9999。您将在此范围以外的几年中遇到问题，例如解码错误或使用SQLite日期和时间功能的无效日期计算。
某些应用程序可能更喜欢另一种日期格式：
T分离器。Date往返。选择不同的日期格式之前，您应该三思而后行：
Date往返不像乍一看的那样明显的需求。通常，日期通常不会在离开您的应用程序时准确地往返，因为您的应用程序通过使用自己的日期表示（您的应用程序的Android版本，您的应用程序正在与您进行的服务器等）进行通信的其他系统在顶部其中， Date比较至少与浮点比较一样硬和讨厌。日期格式的自定义是明确的。例如：
let date = Date ( )
let timeInterval = date . timeIntervalSinceReferenceDate
try db . execute (
sql : " INSERT INTO player (creationDate, ...) VALUES (?, ...) " ,
arguments : [ timeInterval , ... ] )
if let row = try Row . fetchOne ( db , ... ) {
let timeInterval : TimeInterval = row [ " creationDate " ]
let creationDate = Date ( timeIntervalSinceReferenceDate : timeInterval )
}另请参阅代码记录，以获取更多日期自定义选项，如果要定义具有自定义数据库表示的日期包裹类型，请参见DatabaseValueConvertible 。
DateComponents通过数据级辅助辅助器类型间接支持。
DataBaseadAsedAtecomponents读取来自SQLite支持的所有日期格式的日期组件，并以您选择的格式存储，从HH：MM到Yyyy-MM-DD HH：MM：MM：SSSSSS。
警告：有效年的范围为0000-9999。您将在此范围以外的几年中遇到问题，例如解码错误或使用SQLite日期和时间功能的无效日期计算。有关更多信息，请参见日期。
像其他值一样，可以从数据库中存储和获取数据级数：
let components = DateComponents ( )
components . year = 1973
components . month = 9
components . day = 18
// Store "1973-09-18"
let dbComponents = DatabaseDateComponents ( components , format : . YMD )
try db . execute (
sql : " INSERT INTO player (birthDate, ...) VALUES (?, ...) " ,
arguments : [ dbComponents , ... ] )
// Read "1973-09-18"
let row = try Row . fetchOne ( db , sql : " SELECT birthDate ... " ) !
let dbComponents : DatabaseDateComponents = row [ " birthDate " ]
dbComponents . format // .YMD (the actual format found in the database)
dbComponents . dateComponents // DateComponents像其他值一样，可以从数据库中存储和获取NSNUMBER和十进制。
这是GRDB如何支持SQLITE支持的各种数据类型：
| 整数 | 双倍的 | 细绳 | |
|---|---|---|---|
| nsnumber | 读 /写 | 读 /写 | 读 |
| nsdecimalnumber | 读 /写 | 读 /写 | 读 |
| 十进制 | 读 | 读 | 读 /写 |
这三种类型都可以解码数据库整数并加倍：
let number = try NSNumber . fetchOne ( db , sql : " SELECT 10 " ) // NSNumber
let number = try NSDecimalNumber . fetchOne ( db , sql : " SELECT 1.23 " ) // NSDecimalNumber
let number = try Decimal . fetchOne ( db , sql : " SELECT -100 " ) // Decimal这三种类型都将数据库字符串解码为十进制数字：
let number = try NSNumber . fetchOne ( db , sql : " SELECT '10' " ) // NSDecimalNumber (sic)
let number = try NSDecimalNumber . fetchOne ( db , sql : " SELECT '1.23' " ) // NSDecimalNumber
let number = try Decimal . fetchOne ( db , sql : " SELECT '-100' " ) // Decimal NSNumber和NSDecimalNumber在数据库中发送了64位签名的整数和双打：
// INSERT INTO transfer VALUES (10)
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ NSNumber ( value : 10 ) ] )
// INSERT INTO transfer VALUES (10.0)
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ NSNumber ( value : 10.0 ) ] )
// INSERT INTO transfer VALUES (10)
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ NSDecimalNumber ( string : " 10.0 " ) ] )
// INSERT INTO transfer VALUES (10.5)
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ NSDecimalNumber ( string : " 10.5 " ) ] )警告：由于SQLITE不支持小数数字，因此发送非整数
NSDecimalNumber可能会导致转换期间的精确度损失。您可能更
NSDecimalNumber：
- 而是发送
Decimal（数据库中的那些存储十进制字符串）。- 而是发送整数（例如，存储数美的数量而不是欧元的金额）。
Decimal在数据库中发送小数字符串：
// INSERT INTO transfer VALUES ('10')
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ Decimal ( 10 ) ] )
// INSERT INTO transfer VALUES ('10.5')
try db . execute ( sql : " INSERT INTO transfer VALUES (?) " , arguments : [ Decimal ( string : " 10.5 " ) ! ] )就像其他值一样，可以从数据库中存储和获取UUID 。
GRDB将UUID存储为16个数据斑点，并将它们从16个Bytes数据斑点和字符串中解码，例如“ E621EF8-C36C-495A-93FC-0C247A3E3E6E5F”。
Swift Enums和通常采用可原始协议的所有类型都可以像它们的原始值一样从数据库中存储和获取：
enum Color : Int {
case red , white , rose
}
enum Grape : String {
case chardonnay , merlot , riesling
}
// Declare empty DatabaseValueConvertible adoption
extension Color : DatabaseValueConvertible { }
extension Grape : DatabaseValueConvertible { }
// Store
try db . execute (
sql : " INSERT INTO wine (grape, color) VALUES (?, ?) " ,
arguments : [ Grape . merlot , Color . red ] )
// Read
let rows = try Row . fetchCursor ( db , sql : " SELECT * FROM wine " )
while let row = try rows . next ( ) {
let grape : Grape = row [ " grape " ]
let color : Color = row [ " color " ]
}当数据库值与任何枚举情况不匹配时，您会遇到致命错误。可以使用数据库值类型来避免这种致命错误：
let row = try Row . fetchOne ( db , sql : " SELECT 'syrah' " ) !
row [ 0 ] as String // "syrah"
row [ 0 ] as Grape ? // fatal error: could not convert "syrah" to Grape.
row [ 0 ] as Grape // fatal error: could not convert "syrah" to Grape.
let dbValue : DatabaseValue = row [ 0 ]
if dbValue . isNull {
// Handle NULL
} else if let grape = Grape . fromDatabaseValue ( dbValue ) {
// Handle valid grape
} else {
// Handle unknown grape
} SQLITE可让您定义SQL功能和聚合。
自定义SQL函数或聚合扩展了SQLITE：
SELECT reverse(name) FROM player; -- custom function
SELECT maxLength(name) FROM player; -- custom aggregateDatabaseFunction
函数参数采用数据库值数组，并返回任何有效的值（bool，int，string，date，swift枚举等）。
当功能“纯”时，SQLite有机会执行其他优化，这意味着他们的结果仅取决于他们的论点。因此，请确保在可能的情况下将纯参数设置为真。
let reverse = DatabaseFunction ( " reverse " , argumentCount : 1 , pure : true ) { ( values : [ DatabaseValue ] ) in
// Extract string value, if any...
guard let string = String . fromDatabaseValue ( values [ 0 ] ) else {
return nil
}
// ... and return reversed string:
return String ( string . reversed ( ) )
}您可以通过其配置使数据库连接可用：
var config = Configuration ( )
config . prepareDatabase { db in
db . add ( function : reverse )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )
try dbQueue . read { db in
// "oof"
try String . fetchOne ( db , sql : " SELECT reverse('foo') " ) !
}功能可以采用可变数量的参数：
如果您不提供任何明确的参数量，则该函数可以采用任何数量的参数：
let averageOf = DatabaseFunction ( " averageOf " , pure : true ) { ( values : [ DatabaseValue ] ) in
let doubles = values . compactMap { Double . fromDatabaseValue ( $0 ) }
return doubles . reduce ( 0 , + ) / Double ( doubles . count )
}
db . add ( function : averageOf )
// 2.0
try Double . fetchOne ( db , sql : " SELECT averageOf(1, 2, 3) " ) !功能可以投掷：
let sqrt = DatabaseFunction ( " sqrt " , argumentCount : 1 , pure : true ) { ( values : [ DatabaseValue ] ) in
guard let double = Double . fromDatabaseValue ( values [ 0 ] ) else {
return nil
}
guard double >= 0 else {
throw DatabaseError ( message : " invalid negative number " )
}
return sqrt ( double )
}
db . add ( function : sqrt )
// SQLite error 1 with statement `SELECT sqrt(-1)`: invalid negative number
try Double . fetchOne ( db , sql : " SELECT sqrt(-1) " ) !在查询接口中使用自定义功能：
// SELECT reverseString("name") FROM player
Player . select ( reverseString ( nameColumn ) )GRDB具有内置SQL函数，执行Unicode-Aware String转换。请参阅Unicode。
DatabaseFunction ， DatabaseAggregate
在注册自定义汇总之前，您需要定义一种采用DatabaseAggregate协议的类型：
protocol DatabaseAggregate {
// Initializes an aggregate
init ( )
// Called at each step of the aggregation
mutating func step ( _ dbValues : [ DatabaseValue ] ) throws
// Returns the final result
func finalize ( ) throws -> DatabaseValueConvertible ?
}例如：
struct MaxLength : DatabaseAggregate {
var maxLength : Int = 0
mutating func step ( _ dbValues : [ DatabaseValue ] ) {
// At each step, extract string value, if any...
guard let string = String . fromDatabaseValue ( dbValues [ 0 ] ) else {
return
}
// ... and update the result
let length = string . count
if length > maxLength {
maxLength = length
}
}
func finalize ( ) -> DatabaseValueConvertible ? {
maxLength
}
}
let maxLength = DatabaseFunction (
" maxLength " ,
argumentCount : 1 ,
pure : true ,
aggregate : MaxLength . self )像自定义SQL函数一样，您可以通过其配置使数据库连接可用：
var config = Configuration ( )
config . prepareDatabase { db in
db . add ( function : maxLength )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )
try dbQueue . read { db in
// Some Int
try Int . fetchOne ( db , sql : " SELECT maxLength(name) FROM player " ) !
}汇总的step方法采用了一系列数据库值。此数组包含与参数参数（或省略参数数时的任何数量值的值）一样多的值。
汇总的finalize方法返回最终的汇总值（bool，int，string，date，swift枚举等）。
当聚集体为“纯”时，SQLITE有机会进行额外的优化，这意味着它们的结果仅取决于其输入。因此，请确保在可能的情况下将纯参数设置为真。
在查询接口中使用自定义聚合物：
// SELECT maxLength("name") FROM player
let request = Player . select ( maxLength . apply ( nameColumn ) )
try Int . fetchOne ( db , request ) // Int? 如果不是所有的sqlite API都在GRDB中暴露，则仍然可以使用sqlite c接口并调用sqlite c函数。
要从SQLCipher或System SQLite访问C SQLITE函数，您需要执行额外的导入：
import SQLite3 // System SQLite
import SQLCipher // SQLCipher
let sqliteVersion = String ( cString : sqlite3_libversion ( ) )可以通过Database.sqliteConnection和Statement.sqliteStatement属性：
try dbQueue . read { db in
// The raw pointer to a database connection:
let sqliteConnection = db . sqliteConnection
// The raw pointer to a statement:
let statement = try db . makeStatement ( sql : " SELECT ... " )
let sqliteStatement = statement . sqliteStatement
}笔记
- 这些指针由GRDB拥有：不要关闭GRDB创建的连接或最终确定语句。
- GRDB以“多线程模式”打开SQLite连接，这（奇怪的是）意味着它们不是线程安全。确保您触摸其专用调度队列中的原始数据库和语句。
- 使用RAW SQLITE C接口自身风险。 GRDB不会阻止您射击自己。
在SQLite API之上，GRDB提供了协议，可以帮助将数据库行作为名为“记录”的常规对象操作：
try dbQueue . write { db in
if var place = try Place . fetchOne ( db , id : 1 ) {
place . isFavorite = true
try place . update ( db )
}
}当然，您需要打开数据库连接，然后首先创建数据库表。
要定义记录类型，请定义类型并使用集中功能集的协议扩展。
例如：
struct Player: {
var id: Int64
var name: String
var score: Int
}
// Players can be fetched from the database.
extension Player: FetchableRecord { ... }
// Players can be saved into the database.
extension Player: PersistableRecord { ... }
请参见记录定义的一些示例。
注意：如果您熟悉核心数据的NSManageBject或Realm的对象，则可能会遇到文化冲击：GRDB记录不是唯一的，不要自动更新，并且不要懒惰。这既是目的，也是面向协议的编程的结果。
提示：设计记录类型指南的建议实践提供了一般指导。
提示：有关使用记录的示例应用程序，请参阅“演示应用程序”。
概述
协议和记录类
RETURNING子句要在数据库中插入记录，请调用insert方法：
let player = Player ( name : " Arthur " , email : " [email protected] " )
try player . insert ( db ) insert可用于采用PersistableRecord协议的类型。
要从数据库中获取记录，请调用一种获取方法：
let arthur = try Player . fetchOne ( db , // Player?
sql : " SELECT * FROM players WHERE name = ? " ,
arguments : [ " Arthur " ] )
let bestPlayers = try Player // [Player]
. order ( Column ( " score " ) . desc )
. limit ( 10 )
. fetchAll ( db )
let spain = try Country . fetchOne ( db , id : " ES " ) // Country?
let italy = try Country . find ( db , id : " IT " ) // Country从RAW SQL获取可用于采用FetchableRecord协议的类型。
使用查询接口无SQL的获取可用于采用FetchableRecord和TableRecord协议的类型。
要更新数据库中的记录，请调用update方法：
var player : Player = ...
player . score = 1000
try player . update ( db )可以避免无用的更新：
// does not hit the database if score has not changed
try player . updateChanges ( db ) {
$0 . score = 1000
}请参阅查询接口以获取批处理更新：
try Player
. filter ( Column ( " team " ) == " red " )
. updateAll ( db , Column ( " score " ) += 1 )更新方法可用于采用PersistableRecord协议的类型。 TableRecord协议上可用批处理更新。
要删除数据库中的记录，请调用delete方法：
let player : Player = ...
try player . delete ( db )您还可以通过主密钥，唯一密钥删除或执行批处理删除（请参阅删除请求）：
try Player . deleteOne ( db , id : 1 )
try Player . deleteOne ( db , key : [ " email " : " [email protected] " ] )
try Country . deleteAll ( db , ids : [ " FR " , " US " ] )
try Player
. filter ( Column ( " email " ) == nil )
. deleteAll ( db )删除方法可用于采用PersistableRecord协议的类型。批处理删除可在TableEcord协议上可用。
要计算记录，请调用fetchCount方法：
let playerCount : Int = try Player . fetchCount ( db )
let playerWithEmailCount : Int = try Player
. filter ( Column ( " email " ) == nil )
. fetchCount ( db ) fetchCount适用于采用TableCord协议的类型。
详细信息如下：
GRDB带有三个记录协议。根据您要扩展类型的能力，您自己的类型将采用其中一种或几种。
FetchablEcord能够解码数据库行。
struct Place : FetchableRecord { ... }
let places = try dbQueue . read { db in
try Place . fetchAll ( db , sql : " SELECT * FROM place " )
}提示：
FetchableRecord可以从标准Decodable协议中得出其实现。有关更多信息，请参见编码记录。
FetchableRecord可以解码数据库行，但无法为您构建SQL请求。为此，您还需要TableRecord ：
tableRecord能够生成SQL查询：
struct Place : TableRecord { ... }
let placeCount = try dbQueue . read { db in
// Generates and runs `SELECT COUNT(*) FROM place`
try Place . fetchCount ( db )
}当一种类型同时采用TableRecord和FetchableRecord时，它可以从这些请求中加载：
struct Place : TableRecord , FetchableRecord { ... }
try dbQueue . read { db in
let places = try Place . order ( Column ( " title " ) ) . fetchAll ( db )
let paris = try Place . fetchOne ( id : 1 )
}PersistableCord能够写：它可以在数据库中创建，更新和删除行：
struct Place : PersistableRecord { ... }
try dbQueue . write { db in
try Place . delete ( db , id : 1 )
try Place ( ... ) . insert ( db )
}持久记录还可以与其他记录进行比较，并避免使用无用的数据库更新。
提示：
PersistableRecord可以从标准Encodable协议中得出其实现。有关更多信息，请参见编码记录。
FetchableRecord
FetchableRecord协议将获取方法授予可以从数据库行构建的任何类型：
protocol FetchableRecord {
/// Row initializer
init ( row : Row ) throws
}例如：
struct Place {
var id : Int64 ?
var title : String
var coordinate : CLLocationCoordinate2D
}
extension Place : FetchableRecord {
init ( row : Row ) {
id = row [ " id " ]
title = row [ " title " ]
coordinate = CLLocationCoordinate2D (
latitude : row [ " latitude " ] ,
longitude : row [ " longitude " ] )
}
}行还接受列表：
extension Place : FetchableRecord {
enum Columns : String , ColumnExpression {
case id , title , latitude , longitude
}
init ( row : Row ) {
id = row [ Columns . id ]
title = row [ Columns . title ]
coordinate = CLLocationCoordinate2D (
latitude : row [ Columns . latitude ] ,
longitude : row [ Columns . longitude ] )
}
}有关row[]订阅的更多信息，请参见列值。
当您的记录类型采用标准可解码协议时，您不必为init(row:)提供实现。有关更多信息，请参见编码记录：
// That's all
struct Player : Decodable , FetchableRecord {
var id : Int64
var name : String
var score : Int
}FetchableRecord允许从SQL查询获取采用类型：
try Place . fetchCursor ( db , sql : " SELECT ... " , arguments : ... ) // A Cursor of Place
try Place . fetchAll ( db , sql : " SELECT ... " , arguments : ... ) // [Place]
try Place . fetchSet ( db , sql : " SELECT ... " , arguments : ... ) // Set<Place>
try Place . fetchOne ( db , sql : " SELECT ... " , arguments : ... ) // Place?有关fetchCursor ， fetchAll ， fetchSet和fetchOne方法的信息，请参见获取方法。有关查询参数的更多信息，请参见StatementArguments 。
注意：出于绩效原因，在提取查询的迭代期间，同一行参数
init(row:)重复使用。如果要保留该行供以后使用，请确保存储一个副本：self.row = row.copy()。
注意：
FetchableRecord.init(row:)initializer符合大多数应用程序的需求。但是，某些应用比其他应用更高。当FetchableCord无法完全提供所需的支持时，请查看《 Beyond Fetchablerecord》一章。
TableRecord
TableRecord协议为您生成SQL：
protocol TableRecord {
static var databaseTableName : String { get }
static var databaseSelection : [ any SQLSelectable ] { get }
} databaseSelection类型属性是可选的，并在请求章节选择的列中进行了记录。
databaseTableName类型属性是数据库表的名称。默认情况下，它是从类型名称派生的：
struct Place : TableRecord { }
print ( Place . databaseTableName ) // prints "place"例如：
placecountrypostalAddresshttpRequesttoefl您仍然可以提供自定义表名称：
struct Place : TableRecord {
static let databaseTableName = " location "
}
print ( Place . databaseTableName ) // prints "location"当一种类型同时采用tableecord和fetchableRecord时，可以使用查询接口获取它：
// SELECT * FROM place WHERE name = 'Paris'
let paris = try Place . filter ( nameColumn == " Paris " ) . fetchOne ( db )TableRecord还可以获取主要键和独特的键：请参阅按键获取并测试记录存在。
EncodableRecord ， MutablePersistableRecord ， PersistableRecord
GRDB记录类型可以在数据库中创建，更新和删除行。
这些能力由三个方案授予：
// Defines how a record encodes itself into the database
protocol EncodableRecord {
/// Defines the values persisted in the database
func encode ( to container : inout PersistenceContainer ) throws
}
// Adds persistence methods
protocol MutablePersistableRecord : TableRecord , EncodableRecord {
/// Optional method that lets your adopting type store its rowID upon
/// successful insertion. Don't call it directly: it is called for you.
mutating func didInsert ( _ inserted : InsertionSuccess )
}
// Adds immutability
protocol PersistableRecord : MutablePersistableRecord {
/// Non-mutating version of the optional didInsert(_:)
func didInsert ( _ inserted : InsertionSuccess )
}是的，三个协议而不是一个协议。这是您选择一个或另一个的方式：
如果您的类型是类，请选择PersistableRecord 。最重要的是，如果数据库表具有自动插入的主键，则实施didInsert(_:)
如果您的类型是结构，并且数据库表具有自动插入的主键，请选择MutablePersistableRecord ，然后实现didInsert(_:) 。
否则，选择PersistableRecord ，然后忽略didInsert(_:) 。
The encode(to:) method defines which values (Bool, Int, String, Date, Swift enums, etc.) are assigned to database columns.
The optional didInsert method lets the adopting type store its rowID after successful insertion, and is only useful for tables that have an auto-incremented primary key. It is called from a protected dispatch queue, and serialized with all database updates.
例如：
extension Place : MutablePersistableRecord {
/// The values persisted in the database
func encode ( to container : inout PersistenceContainer ) {
container [ " id " ] = id
container [ " title " ] = title
container [ " latitude " ] = coordinate . latitude
container [ " longitude " ] = coordinate . longitude
}
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}
var paris = Place (
id : nil ,
title : " Paris " ,
coordinate : CLLocationCoordinate2D ( latitude : 48.8534100 , longitude : 2.3488000 ) )
try paris . insert ( db )
paris . id // some valuePersistence containers also accept column enums:
extension Place : MutablePersistableRecord {
enum Columns : String , ColumnExpression {
case id , title , latitude , longitude
}
func encode ( to container : inout PersistenceContainer ) {
container [ Columns . id ] = id
container [ Columns . title ] = title
container [ Columns . latitude ] = coordinate . latitude
container [ Columns . longitude ] = coordinate . longitude
}
} When your record type adopts the standard Encodable protocol, you don't have to provide the implementation for encode(to:) . See Codable Records for more information:
// That's all
struct Player : Encodable , MutablePersistableRecord {
var id : Int64 ?
var name : String
var score : Int
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}Types that adopt the PersistableRecord protocol are given methods that insert, update, and delete:
// INSERT
try place . insert ( db )
let insertedPlace = try place . inserted ( db ) // non-mutating
// UPDATE
try place . update ( db )
try place . update ( db , columns : [ " title " ] )
// Maybe UPDATE
try place . updateChanges ( db , from : otherPlace )
try place . updateChanges ( db ) { $0 . isFavorite = true }
// INSERT or UPDATE
try place . save ( db )
let savedPlace = place . saved ( db ) // non-mutating
// UPSERT
try place . upsert ( db )
let insertedPlace = place . upsertAndFetch ( db )
// DELETE
try place . delete ( db )
// EXISTENCE CHECK
let exists = try place . exists ( db )See Upsert below for more information about upserts.
The TableRecord protocol comes with batch operations :
// UPDATE
try Place . updateAll ( db , ... )
// DELETE
try Place . deleteAll ( db )
try Place . deleteAll ( db , ids : ... )
try Place . deleteAll ( db , keys : ... )
try Place . deleteOne ( db , id : ... )
try Place . deleteOne ( db , key : ... )For more information about batch updates, see Update Requests.
All persistence methods can throw a DatabaseError.
update and updateChanges throw RecordError if the database does not contain any row for the primary key of the record.
save makes sure your values are stored in the database. It performs an UPDATE if the record has a non-null primary key, and then, if no row was modified, an INSERT. It directly performs an INSERT if the record has no primary key, or a null primary key.
delete and deleteOne returns whether a database row was deleted or not. deleteAll returns the number of deleted rows. updateAll returns the number of updated rows. updateChanges returns whether a database row was updated or not.
All primary keys are supported , including composite primary keys that span several columns, and the hidden rowid column.
To customize persistence methods , you provide Persistence Callbacks, described below. Do not attempt at overriding the ready-made persistence methods.
UPSERT is an SQLite feature that causes an INSERT to behave as an UPDATE or a no-op if the INSERT would violate a uniqueness constraint (primary key or unique index).
Note : Upsert apis are available from SQLite 3.35.0+: iOS 15.0+, macOS 12.0+, tvOS 15.0+, watchOS 8.0+, or with a custom SQLite build or SQLCipher.
Note : With regard to persistence callbacks, an upsert behaves exactly like an insert. In particular: the
aroundInsert(_:)anddidInsert(_:)callbacks reports the rowid of the inserted or updated row;willUpdate,aroundUdate,didUdateare not called.
PersistableRecord provides three upsert methods:
upsert(_:)
Inserts or updates a record.
The upsert behavior is triggered by a violation of any uniqueness constraint on the table (primary key or unique index). In case of conflict, all columns but the primary key are overwritten with the inserted values:
struct Player : Encodable , PersistableRecord {
var id : Int64
var name : String
var score : Int
}
// INSERT INTO player (id, name, score)
// VALUES (1, 'Arthur', 1000)
// ON CONFLICT DO UPDATE SET
// name = excluded.name,
// score = excluded.score
let player = Player ( id : 1 , name : " Arthur " , score : 1000 )
try player . upsert ( db ) upsertAndFetch(_:onConflict:doUpdate:) (requires FetchableRecord conformance)
Inserts or updates a record, and returns the upserted record.
The onConflict and doUpdate arguments let you further control the upsert behavior. Make sure you check the SQLite UPSERT documentation for detailed information.
onConflict : the "conflict target" is the array of columns in the uniqueness constraint (primary key or unique index) that triggers the upsert.
If empty (the default), all uniqueness constraint are considered.
doUpdate : a closure that returns columns assignments to perform in case of conflict. Other columns are overwritten with the inserted values.
By default, all inserted columns but the primary key and the conflict target are overwritten.
In the example below, we upsert the new vocabulary word "jovial". It is inserted if that word is not already in the dictionary. Otherwise, count is incremented, isTainted is not overwritten, and kind is overwritten:
// CREATE TABLE vocabulary(
// word TEXT NOT NULL PRIMARY KEY,
// kind TEXT NOT NULL,
// isTainted BOOLEAN DEFAULT 0,
// count INT DEFAULT 1))
struct Vocabulary : Encodable , PersistableRecord {
var word : String
var kind : String
var isTainted : Bool
}
// INSERT INTO vocabulary(word, kind, isTainted)
// VALUES('jovial', 'adjective', 0)
// ON CONFLICT(word) DO UPDATE SET
// count = count + 1, -- on conflict, count is incremented
// kind = excluded.kind -- on conflict, kind is overwritten
// RETURNING *
let vocabulary = Vocabulary ( word : " jovial " , kind : " adjective " , isTainted : false )
let upserted = try vocabulary . upsertAndFetch (
db , onConflict : [ " word " ] ,
doUpdate : { _ in
[ Column ( " count " ) += 1 , // on conflict, count is incremented
Column ( " isTainted " ) . noOverwrite ] // on conflict, isTainted is NOT overwritten
} ) The doUpdate closure accepts an excluded TableAlias argument that refers to the inserted values that trigger the conflict. You can use it to specify an explicit overwrite, or to perform a computation. In the next example, the upsert keeps the maximum date in case of conflict:
// INSERT INTO message(id, text, date)
// VALUES(...)
// ON CONFLICT DO UPDATE SET
// text = excluded.text,
// date = MAX(date, excluded.date)
// RETURNING *
let upserted = try message . upsertAndFetch ( doUpdate : { excluded in
// keep the maximum date in case of conflict
[ Column ( " date " ) . set ( to : max ( Column ( " date " ) , excluded [ " date " ] ) ) ]
} ) upsertAndFetch(_:as:onConflict:doUpdate:) (does not require FetchableRecord conformance)
This method is identical to upsertAndFetch(_:onConflict:doUpdate:) described above, but you can provide a distinct FetchableRecord record type as a result, in order to specify the returned columns.
RETURNING clause SQLite is able to return values from a inserted, updated, or deleted row, with the RETURNING clause.
Note : Support for the
RETURNINGclause is available from SQLite 3.35.0+: iOS 15.0+, macOS 12.0+, tvOS 15.0+, watchOS 8.0+, or with a custom SQLite build or SQLCipher.
The RETURNING clause helps dealing with database features such as auto-incremented ids, default values, and generated columns. You can, for example, insert a few columns and fetch the default or generated ones in one step.
GRDB uses the RETURNING clause in all persistence methods that contain AndFetch in their name.
For example, given a database table with an auto-incremented primary key and a default score:
try dbQueue . write { db in
try db . execute ( sql : """
CREATE TABLE player(
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL,
score INTEGER NOT NULL DEFAULT 1000)
""" )
}You can define a record type with full database information, and another partial record type that deals with a subset of columns:
// A player with full database information
struct Player : Codable , PersistableRecord , FetchableRecord {
var id : Int64
var name : String
var score : Int
}
// A partial player
struct PartialPlayer : Encodable , PersistableRecord {
static let databaseTableName = " player "
var name : String
}And now you can get a full player by inserting a partial one:
try dbQueue . write { db in
let partialPlayer = PartialPlayer ( name : " Alice " )
// INSERT INTO player (name) VALUES ('Alice') RETURNING *
let player = try partialPlayer . insertAndFetch ( db , as : Player . self )
print ( player . id ) // The inserted id
print ( player . name ) // The inserted name
print ( player . score ) // The default score
} For extra precision, you can select only the columns you need, and fetch the desired value from the provided prepared Statement :
try dbQueue . write { db in
let partialPlayer = PartialPlayer ( name : " Alice " )
// INSERT INTO player (name) VALUES ('Alice') RETURNING score
let score = try partialPlayer . insertAndFetch ( db , selection : [ Column ( " score " ) ] ) { statement in
try Int . fetchOne ( statement )
}
print ( score ) // Prints 1000, the default score
} There are other similar persistence methods, such as upsertAndFetch , saveAndFetch , updateAndFetch , updateChangesAndFetch , etc. They all behave like upsert , save , update , updateChanges , except that they return saved values.例如：
// Save and return the saved player
let savedPlayer = try player . saveAndFetch ( db ) See Persistence Methods, Upsert, and updateChanges methods for more information.
Batch operations can return updated or deleted values:
Warning : Make sure you check the documentation of the
RETURNINGclause, which describes important limitations and caveats for batch operations.
let request = Player . filter ( ... ) ...
// Fetch all deleted players
// DELETE FROM player RETURNING *
let deletedPlayers = try request . deleteAndFetchAll ( db ) // [Player]
// Fetch a selection of columns from the deleted rows
// DELETE FROM player RETURNING name
let statement = try request . deleteAndFetchStatement ( db , selection : [ Column ( " name " ) ] )
let deletedNames = try String . fetchSet ( statement )
// Fetch all updated players
// UPDATE player SET score = score + 10 RETURNING *
let updatedPlayers = try request . updateAndFetchAll ( db , [ Column ( " score " ) += 10 ] ) // [Player]
// Fetch a selection of columns from the updated rows
// UPDATE player SET score = score + 10 RETURNING score
let statement = try request . updateAndFetchStatement (
db , [ Column ( " score " ) += 10 ] ,
select : [ Column ( " score " ) ] )
let updatedScores = try Int . fetchAll ( statement )Your custom type may want to perform extra work when the persistence methods are invoked.
To this end, your record type can implement persistence callbacks . Callbacks are methods that get called at certain moments of a record's life cycle. With callbacks it is possible to write code that will run whenever an record is inserted, updated, or deleted.
In order to use a callback method, you need to provide its implementation. For example, a frequently used callback is didInsert , in the case of auto-incremented database ids:
struct Player : MutablePersistableRecord {
var id : Int64 ?
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}
try dbQueue . write { db in
var player = Player ( id : nil , ... )
try player . insert ( db )
print ( player . id ) // didInsert was called: prints some non-nil id
}Callbacks can also help implementing record validation:
struct Link : PersistableRecord {
var url : URL
func willSave ( _ db : Database ) throws {
if url . host == nil {
throw ValidationError ( " url must be absolute. " )
}
}
}
try link . insert ( db ) // Calls the willSave callback
try link . update ( db ) // Calls the willSave callback
try link . save ( db ) // Calls the willSave callback
try link . upsert ( db ) // Calls the willSave callback Here is a list with all the available persistence callbacks, listed in the same order in which they will get called during the respective operations:
Inserting a record (all record.insert and record.upsert methods)
willSavearoundSavewillInsertaroundInsertdidInsertdidSave Updating a record (all record.update methods)
willSavearoundSavewillUpdatearoundUpdatedidUpdatedidSave Deleting a record (only the record.delete(_:) method)
willDeletearoundDeletedidDeleteFor detailed information about each callback, check the reference.
In the MutablePersistableRecord protocol, willInsert and didInsert are mutating methods. In PersistableRecord , they are not mutating.
Note : The
record.save(_:)method performs an UPDATE if the record has a non-null primary key, and then, if no row was modified, an INSERT. It directly performs an INSERT if the record has no primary key, or a null primary key. It triggers update and/or insert callbacks accordingly.Warning : Callbacks are only invoked from persistence methods called on record instances. Callbacks are not invoked when you call a type method, perform a batch operations, or execute raw SQL.
Warning : When a
did***callback is invoked, do not assume that the change is actually persisted on disk, because the database may still be inside an uncommitted transaction. When you need to handle transaction completions, use the afterNextTransaction(onCommit:onRollback:).例如：struct PictureFile : PersistableRecord { var path : String func willDelete ( _ db : Database ) { db . afterNextTransaction { _ in try ? deleteFileOnDisk ( ) } } }
When a record type maps a table with a single-column primary key, it is recommended to have it adopt the standard Identifiable protocol.
struct Player : Identifiable , FetchableRecord , PersistableRecord {
var id : Int64 // fulfills the Identifiable requirement
var name : String
var score : Int
} When id has a database-compatible type (Int64, Int, String, UUID, ...), the Identifiable conformance unlocks type-safe record and request methods:
let player = try Player . find ( db , id : 1 ) // Player
let player = try Player . fetchOne ( db , id : 1 ) // Player?
let players = try Player . fetchAll ( db , ids : [ 1 , 2 , 3 ] ) // [Player]
let players = try Player . fetchSet ( db , ids : [ 1 , 2 , 3 ] ) // Set<Player>
let request = Player . filter ( id : 1 )
let request = Player . filter ( ids : [ 1 , 2 , 3 ] )
try Player . deleteOne ( db , id : 1 )
try Player . deleteAll ( db , ids : [ 1 , 2 , 3 ] )Note : Not all record types can be made
Identifiable, and not all tables have a single-column primary key. GRDB provides other methods that deal with primary and unique keys, but they won't check the type of their arguments:// Available on non-Identifiable types try Player . fetchOne ( db , key : 1 ) try Player . fetchOne ( db , key : [ " email " : " [email protected] " ] ) try Country . fetchAll ( db , keys : [ " FR " , " US " ] ) try Citizenship . fetchOne ( db , key : [ " citizenId " : 1 , " countryCode " : " FR " ] ) let request = Player . filter ( key : 1 ) let request = Player . filter ( keys : [ 1 , 2 , 3 ] ) try Player . deleteOne ( db , key : 1 ) try Player . deleteAll ( db , keys : [ 1 , 2 , 3 ] )
Note : It is not recommended to use
Identifiableon record types that use an auto-incremented primary key:// AVOID declaring Identifiable conformance when key is auto-incremented struct Player { var id : Int64 ? // Not an id suitable for Identifiable var name : String var score : Int } extension Player : FetchableRecord , MutablePersistableRecord { // Update auto-incremented id upon successful insertion mutating func didInsert ( _ inserted : InsertionSuccess ) { id = inserted . rowID } }For a detailed rationale, please see issue #1435.
Some database tables have a single-column primary key which is not called "id":
try db . create ( table : " country " ) { t in
t . primaryKey ( " isoCode " , . text )
t . column ( " name " , . text ) . notNull ( )
t . column ( " population " , . integer ) . notNull ( )
} In this case, Identifiable conformance can be achieved, for example, by returning the primary key column from the id property:
struct Country : Identifiable , FetchableRecord , PersistableRecord {
var isoCode : String
var name : String
var population : Int
// Fulfill the Identifiable requirement
var id : String { isoCode }
}
let france = try dbQueue . read { db in
try Country . fetchOne ( db , id : " FR " )
} Record types that adopt an archival protocol (Codable, Encodable or Decodable) get free database support just by declaring conformance to the desired record protocols:
// Declare a record...
struct Player : Codable , FetchableRecord , PersistableRecord {
var name : String
var score : Int
}
// ...and there you go:
try dbQueue . write { db in
try Player ( name : " Arthur " , score : 100 ) . insert ( db )
let players = try Player . fetchAll ( db )
}Codable records encode and decode their properties according to their own implementation of the Encodable and Decodable protocols. Yet databases have specific requirements:
DatabaseValueConvertible protocol).For more information about Codable records, see:
Tip : see the Demo Applications for sample code that uses Codable records.
When a Codable record contains a property that is not a simple value (Bool, Int, String, Date, Swift enums, etc.), that value is encoded and decoded as a JSON string .例如：
enum AchievementColor : String , Codable {
case bronze , silver , gold
}
struct Achievement : Codable {
var name : String
var color : AchievementColor
}
struct Player : Codable , FetchableRecord , PersistableRecord {
var name : String
var score : Int
var achievements : [ Achievement ] // stored in a JSON column
}
try dbQueue . write { db in
// INSERT INTO player (name, score, achievements)
// VALUES (
// 'Arthur',
// 100,
// '[{"color":"gold","name":"Use Codable Records"}]')
let achievement = Achievement ( name : " Use Codable Records " , color : . gold )
let player = Player ( name : " Arthur " , score : 100 , achievements : [ achievement ] )
try player . insert ( db )
} GRDB uses the standard JSONDecoder and JSONEncoder from Foundation. By default, Data values are handled with the .base64 strategy, Date with the .millisecondsSince1970 strategy, and non conforming floats with the .throw strategy.
You can customize the JSON format by implementing those methods:
protocol FetchableRecord {
static func databaseJSONDecoder ( for column : String ) -> JSONDecoder
}
protocol EncodableRecord {
static func databaseJSONEncoder ( for column : String ) -> JSONEncoder
}Tip : Make sure you set the JSONEncoder
sortedKeysoption. This option makes sure that the JSON output is stable. This stability is required for Record Comparison to work as expected, and database observation tools such as ValueObservation to accurately recognize changed records.
By default, Codable Records store their values into database columns that match their coding keys: the teamID property is stored into the teamID column.
This behavior can be overridden, so that you can, for example, store the teamID property into the team_id column:
protocol FetchableRecord {
static var databaseColumnDecodingStrategy : DatabaseColumnDecodingStrategy { get }
}
protocol EncodableRecord {
static var databaseColumnEncodingStrategy : DatabaseColumnEncodingStrategy { get }
}See DatabaseColumnDecodingStrategy and DatabaseColumnEncodingStrategy to learn about all available strategies.
By default, Codable Records encode and decode their Data properties as blobs, and Date and UUID properties as described in the general Date and DateComponents and UUID chapters.
To sum up: dates encode themselves in the "YYYY-MM-DD HH:MM:SS.SSS" format, in the UTC time zone, and decode a variety of date formats and timestamps. UUIDs encode themselves as 16-bytes data blobs, and decode both 16-bytes data blobs and strings such as "E621E1F8-C36C-495A-93FC-0C247A3E6E5F".
Those behaviors can be overridden:
protocol FetchableRecord {
static func databaseDataDecodingStrategy ( for column : String ) -> DatabaseDataDecodingStrategy
static func databaseDateDecodingStrategy ( for column : String ) -> DatabaseDateDecodingStrategy
}
protocol EncodableRecord {
static func databaseDataEncodingStrategy ( for column : String ) -> DatabaseDataEncodingStrategy
static func databaseDateEncodingStrategy ( for column : String ) -> DatabaseDateEncodingStrategy
static func databaseUUIDEncodingStrategy ( for column : String ) -> DatabaseUUIDEncodingStrategy
}See DatabaseDataDecodingStrategy, DatabaseDateDecodingStrategy, DatabaseDataEncodingStrategy, DatabaseDateEncodingStrategy, and DatabaseUUIDEncodingStrategy to learn about all available strategies.
There is no customization of uuid decoding, because UUID can already decode all its encoded variants (16-bytes blobs and uuid strings, both uppercase and lowercase).
Customized coding strategies apply:
fetchOne(_:id:) , filter(id:) , deleteAll(_:keys:) , etc.They do not apply in other requests based on data, date, or uuid values.
So make sure that those are properly encoded in your requests.例如：
struct Player : Codable , FetchableRecord , PersistableRecord , Identifiable {
// UUIDs are stored as strings
static func databaseUUIDEncodingStrategy ( for column : String ) -> DatabaseUUIDEncodingStrategy {
. uppercaseString
}
var id : UUID
...
}
try dbQueue . write { db in
let uuid = UUID ( )
let player = Player ( id : uuid , ... )
// OK: inserts a player in the database, with a string uuid
try player . insert ( db )
// OK: performs a string-based query, finds the inserted player
_ = try Player . filter ( id : uuid ) . fetchOne ( db )
// NOT OK: performs a blob-based query, fails to find the inserted player
_ = try Player . filter ( Column ( " id " ) == uuid ) . fetchOne ( db )
// OK: performs a string-based query, finds the inserted player
_ = try Player . filter ( Column ( " id " ) == uuid . uuidString ) . fetchOne ( db )
} Your Codable Records can be stored in the database, but they may also have other purposes. In this case, you may need to customize their implementations of Decodable.init(from:) and Encodable.encode(to:) , depending on the context.
The standard way to provide such context is the userInfo dictionary. Implement those properties:
protocol FetchableRecord {
static var databaseDecodingUserInfo : [ CodingUserInfoKey : Any ] { get }
}
protocol EncodableRecord {
static var databaseEncodingUserInfo : [ CodingUserInfoKey : Any ] { get }
}For example, here is a Player type that customizes its decoding:
// A key that holds a decoder's name
let decoderName = CodingUserInfoKey ( rawValue : " decoderName " ) !
struct Player : FetchableRecord , Decodable {
init ( from decoder : Decoder ) throws {
// Print the decoder name
let decoderName = decoder . userInfo [ decoderName ] as? String
print ( " Decoded from ( decoderName ?? " unknown decoder " ) " )
...
}
}You can have a specific decoding from JSON...
// prints "Decoded from JSON"
let decoder = JSONDecoder ( )
decoder . userInfo = [ decoderName : " JSON " ]
let player = try decoder . decode ( Player . self , from : jsonData )... and another one from database rows:
extension Player : FetchableRecord {
static var databaseDecodingUserInfo : [ CodingUserInfoKey : Any ] {
[ decoderName : " database row " ]
}
}
// prints "Decoded from database row"
let player = try Player . fetchOne ( db , ... )Note : make sure the
databaseDecodingUserInfoanddatabaseEncodingUserInfoproperties are explicitly declared as[CodingUserInfoKey: Any]. If they are not, the Swift compiler may silently miss the protocol requirement, resulting in sticky empty userInfo.
Codable types are granted with a CodingKeys enum. You can use them to safely define database columns:
struct Player : Codable {
var id : Int64
var name : String
var score : Int
}
extension Player : FetchableRecord , PersistableRecord {
enum Columns {
static let id = Column ( CodingKeys . id )
static let name = Column ( CodingKeys . name )
static let score = Column ( CodingKeys . score )
}
}See the query interface and Recommended Practices for Designing Record Types for further information.
Records that adopt the EncodableRecord protocol can compare against other records, or against previous versions of themselves.
This helps avoiding costly UPDATE statements when a record has not been edited.
updateChanges MethodsdatabaseEquals MethoddatabaseChanges and hasDatabaseChanges MethodsupdateChanges Methods The updateChanges methods perform a database update of the changed columns only (and does nothing if record has no change).
updateChanges(_:from:)
This method lets you compare two records:
if let oldPlayer = try Player . fetchOne ( db , id : 42 ) {
var newPlayer = oldPlayer
newPlayer . score = 100
if try newPlayer . updateChanges ( db , from : oldPlayer ) {
print ( " player was modified, and updated in the database " )
} else {
print ( " player was not modified, and database was not hit " )
}
} updateChanges(_:modify:)
This method lets you update a record in place:
if var player = try Player . fetchOne ( db , id : 42 ) {
let modified = try player . updateChanges ( db ) {
$0 . score = 100
}
if modified {
print ( " player was modified, and updated in the database " )
} else {
print ( " player was not modified, and database was not hit " )
}
}databaseEquals MethodThis method returns whether two records have the same database representation:
let oldPlayer : Player = ...
var newPlayer : Player = ...
if newPlayer . databaseEquals ( oldPlayer ) == false {
try newPlayer . save ( db )
}Note : The comparison is performed on the database representation of records. As long as your record type adopts the EncodableRecord protocol, you don't need to care about Equatable.
databaseChanges and hasDatabaseChanges Methods databaseChanges(from:) returns a dictionary of differences between two records:
let oldPlayer = Player ( id : 1 , name : " Arthur " , score : 100 )
let newPlayer = Player ( id : 1 , name : " Arthur " , score : 1000 )
for (column , oldValue ) in try newPlayer . databaseChanges ( from : oldPlayer ) {
print ( " ( column ) was ( oldValue ) " )
}
// prints "score was 100"For an efficient algorithm which synchronizes the content of a database table with a JSON payload, check groue/SortedDifference.
GRDB records come with many default behaviors, that are designed to fit most situations. Many of those defaults can be customized for your specific needs:
player.insert(db)INSERT OR REPLACE queries, and generally define what happens when a persistence method violates a unique index.Player.fetchAll(db) .Codable Records have a few extra options:
Insertions and updates can create conflicts : for example, a query may attempt to insert a duplicate row that violates a unique index.
Those conflicts normally end with an error. Yet SQLite let you alter the default behavior, and handle conflicts with specific policies. For example, the INSERT OR REPLACE statement handles conflicts with the "replace" policy which replaces the conflicting row instead of throwing an error.
The five different policies are: abort (the default), replace, rollback, fail, and ignore.
SQLite let you specify conflict policies at two different places:
In the definition of the database table:
// CREATE TABLE player (
// id INTEGER PRIMARY KEY AUTOINCREMENT,
// email TEXT UNIQUE ON CONFLICT REPLACE
// )
try db . create ( table : " player " ) { t in
t . autoIncrementedPrimaryKey ( " id " )
t . column ( " email " , . text ) . unique ( onConflict : . replace ) // <--
}
// Despite the unique index on email, both inserts succeed.
// The second insert replaces the first row:
try db . execute ( sql : " INSERT INTO player (email) VALUES (?) " , arguments : [ " [email protected] " ] )
try db . execute ( sql : " INSERT INTO player (email) VALUES (?) " , arguments : [ " [email protected] " ] )In each modification query:
// CREATE TABLE player (
// id INTEGER PRIMARY KEY AUTOINCREMENT,
// email TEXT UNIQUE
// )
try db . create ( table : " player " ) { t in
t . autoIncrementedPrimaryKey ( " id " )
t . column ( " email " , . text ) . unique ( )
}
// Again, despite the unique index on email, both inserts succeed.
try db . execute ( sql : " INSERT OR REPLACE INTO player (email) VALUES (?) " , arguments : [ " [email protected] " ] )
try db . execute ( sql : " INSERT OR REPLACE INTO player (email) VALUES (?) " , arguments : [ " [email protected] " ] ) When you want to handle conflicts at the query level, specify a custom persistenceConflictPolicy in your type that adopts the PersistableRecord protocol. It will alter the INSERT and UPDATE queries run by the insert , update and save persistence methods:
protocol MutablePersistableRecord {
/// The policy that handles SQLite conflicts when records are
/// inserted or updated.
///
/// This property is optional: its default value uses the ABORT
/// policy for both insertions and updates, so that GRDB generate
/// regular INSERT and UPDATE queries.
static var persistenceConflictPolicy : PersistenceConflictPolicy { get }
}
struct Player : MutablePersistableRecord {
static let persistenceConflictPolicy = PersistenceConflictPolicy (
insert : . replace ,
update : . replace )
}
// INSERT OR REPLACE INTO player (...) VALUES (...)
try player . insert ( db )Note : If you specify the
ignorepolicy for inserts, thedidInsertcallback will be called with some random id in case of failed insert. You can detect failed insertions withinsertAndFetch:// How to detect failed `INSERT OR IGNORE`: // INSERT OR IGNORE INTO player ... RETURNING * do { let insertedPlayer = try player . insertAndFetch ( db ) { // Succesful insertion catch RecordError . recordNotFound { // Failed insertion due to IGNORE policy }Note : The
replacepolicy may have to delete rows so that inserts and updates can succeed. Those deletions are not reported to transaction observers (this might change in a future release of SQLite).
Some GRDB users eventually discover that the FetchableRecord protocol does not fit all situations. Use cases that are not well handled by FetchableRecord include:
Your application needs polymorphic row decoding: it decodes some type or another, depending on the values contained in a database row.
Your application needs to decode rows with a context: each decoded value should be initialized with some extra value that does not come from the database.
Since those use cases are not well handled by FetchableRecord, don't try to implement them on top of this protocol: you'll just fight the framework.
We will show below how to declare a record type for the following database table:
try dbQueue . write { db in
try db . create ( table : " place " ) { t in
t . autoIncrementedPrimaryKey ( " id " )
t . column ( " title " , . text ) . notNull ( )
t . column ( " isFavorite " , . boolean ) . notNull ( ) . defaults ( to : false )
t . column ( " longitude " , . double ) . notNull ( )
t . column ( " latitude " , . double ) . notNull ( )
}
}Each one of the three examples below is correct. You will pick one or the other depending on your personal preferences and the requirements of your application:
This is the shortest way to define a record type.
See the Record Protocols Overview, and Codable Records for more information.
struct Place : Codable {
var id : Int64 ?
var title : String
var isFavorite : Bool
private var latitude : CLLocationDegrees
private var longitude : CLLocationDegrees
var coordinate : CLLocationCoordinate2D {
get {
CLLocationCoordinate2D (
latitude : latitude ,
longitude : longitude )
}
set {
latitude = newValue . latitude
longitude = newValue . longitude
}
}
}
// SQL generation
extension Place : TableRecord {
/// The table columns
enum Columns {
static let id = Column ( CodingKeys . id )
static let title = Column ( CodingKeys . title )
static let isFavorite = Column ( CodingKeys . isFavorite )
static let latitude = Column ( CodingKeys . latitude )
static let longitude = Column ( CodingKeys . longitude )
}
}
// Fetching methods
extension Place : FetchableRecord { }
// Persistence methods
extension Place : MutablePersistableRecord {
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}See the Record Protocols Overview for more information.
struct Place {
var id : Int64 ?
var title : String
var isFavorite : Bool
var coordinate : CLLocationCoordinate2D
}
// SQL generation
extension Place : TableRecord {
/// The table columns
enum Columns : String , ColumnExpression {
case id , title , isFavorite , latitude , longitude
}
}
// Fetching methods
extension Place : FetchableRecord {
/// Creates a record from a database row
init ( row : Row ) {
id = row [ Columns . id ]
title = row [ Columns . title ]
isFavorite = row [ Columns . isFavorite ]
coordinate = CLLocationCoordinate2D (
latitude : row [ Columns . latitude ] ,
longitude : row [ Columns . longitude ] )
}
}
// Persistence methods
extension Place : MutablePersistableRecord {
/// The values persisted in the database
func encode ( to container : inout PersistenceContainer ) {
container [ Columns . id ] = id
container [ Columns . title ] = title
container [ Columns . isFavorite ] = isFavorite
container [ Columns . latitude ] = coordinate . latitude
container [ Columns . longitude ] = coordinate . longitude
}
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}This struct derives its persistence methods from the standard Encodable protocol (see Codable Records), but performs optimized row decoding by accessing database columns with numeric indexes.
See the Record Protocols Overview for more information.
struct Place : Encodable {
var id : Int64 ?
var title : String
var isFavorite : Bool
private var latitude : CLLocationDegrees
private var longitude : CLLocationDegrees
var coordinate : CLLocationCoordinate2D {
get {
CLLocationCoordinate2D (
latitude : latitude ,
longitude : longitude )
}
set {
latitude = newValue . latitude
longitude = newValue . longitude
}
}
}
// SQL generation
extension Place : TableRecord {
/// The table columns
enum Columns {
static let id = Column ( CodingKeys . id )
static let title = Column ( CodingKeys . title )
static let isFavorite = Column ( CodingKeys . isFavorite )
static let latitude = Column ( CodingKeys . latitude )
static let longitude = Column ( CodingKeys . longitude )
}
/// Arrange the selected columns and lock their order
static var databaseSelection : [ any SQLSelectable ] {
[
Columns . id ,
Columns . title ,
Columns . favorite ,
Columns . latitude ,
Columns . longitude ,
]
}
}
// Fetching methods
extension Place : FetchableRecord {
/// Creates a record from a database row
init ( row : Row ) {
// For high performance, use numeric indexes that match the
// order of Place.databaseSelection
id = row [ 0 ]
title = row [ 1 ]
isFavorite = row [ 2 ]
coordinate = CLLocationCoordinate2D (
latitude : row [ 3 ] ,
longitude : row [ 4 ] )
}
}
// Persistence methods
extension Place : MutablePersistableRecord {
// Update auto-incremented id upon successful insertion
mutating func didInsert ( _ inserted : InsertionSuccess ) {
id = inserted . rowID
}
}The query interface lets you write pure Swift instead of SQL:
try dbQueue . write { db in
// Update database schema
try db . create ( table : " wine " ) { t in ... }
// Fetch records
let wines = try Wine
. filter ( originColumn == " Burgundy " )
. order ( priceColumn )
. fetchAll ( db )
// Count
let count = try Wine
. filter ( colorColumn == Color . red )
. fetchCount ( db )
// Update
try Wine
. filter ( originColumn == " Burgundy " )
. updateAll ( db , priceColumn *= 0.75 )
// Delete
try Wine
. filter ( corkedColumn == true )
. deleteAll ( db )
}You need to open a database connection before you can query the database.
Please bear in mind that the query interface can not generate all possible SQL queries. You may also prefer writing SQL, and this is just OK. From little snippets to full queries, your SQL skills are welcome:
try dbQueue . write { db in
// Update database schema (with SQL)
try db . execute ( sql : " CREATE TABLE wine (...) " )
// Fetch records (with SQL)
let wines = try Wine . fetchAll ( db ,
sql : " SELECT * FROM wine WHERE origin = ? ORDER BY price " ,
arguments : [ " Burgundy " ] )
// Count (with an SQL snippet)
let count = try Wine
. filter ( sql : " color = ? " , arguments : [ Color . red ] )
. fetchCount ( db )
// Update (with SQL)
try db . execute ( sql : " UPDATE wine SET price = price * 0.75 WHERE origin = 'Burgundy' " )
// Delete (with SQL)
try db . execute ( sql : " DELETE FROM wine WHERE corked " )
}So don't miss the SQL API.
Note : the generated SQL may change between GRDB releases, without notice: don't have your application rely on any specific SQL output.
QueryInterfaceRequest , Table
The query interface requests let you fetch values from the database:
let request = Player . filter ( emailColumn != nil ) . order ( nameColumn )
let players = try request . fetchAll ( db ) // [Player]
let count = try request . fetchCount ( db ) // Int Query interface requests usually start from a type that adopts the TableRecord protocol:
struct Player : TableRecord { ... }
// The request for all players:
let request = Player . all ( )
let players = try request . fetchAll ( db ) // [Player] When you can not use a record type, use Table :
// The request for all rows from the player table:
let table = Table ( " player " )
let request = table . all ( )
let rows = try request . fetchAll ( db ) // [Row]
// The request for all players from the player table:
let table = Table < Player > ( " player " )
let request = table . all ( )
let players = try request . fetchAll ( db ) // [Player]Note : all examples in the documentation below use a record type, but you can always substitute a
Tableinstead.
Next, declare the table columns that you want to use for filtering, or sorting:
let idColumn = Column ( " id " )
let nameColumn = Column ( " name " )You can also declare column enums, if you prefer:
// Columns.id and Columns.name can be used just as
// idColumn and nameColumn declared above.
enum Columns : String , ColumnExpression {
case id
case name
} You can now build requests with the following methods: all , none , select , distinct , filter , matching , group , having , order , reversed , limit , joining , including , with . All those methods return another request, which you can further refine by applying another method: Player.select(...).filter(...).order(...) .
all() , none() : the requests for all rows, or no row.
// SELECT * FROM player
Player . all ( )By default, all columns are selected. See Columns Selected by a Request.
select(...) and select(..., as:) define the selected columns. See Columns Selected by a Request.
// SELECT name FROM player
Player . select ( nameColumn , as : String . self ) annotated(with: expression...) extends the selection.
// SELECT *, (score + bonus) AS total FROM player
Player . annotated ( with : ( scoreColumn + bonusColumn ) . forKey ( " total " ) ) annotated(with: aggregate) extends the selection with association aggregates.
// SELECT team.*, COUNT(DISTINCT player.id) AS playerCount
// FROM team
// LEFT JOIN player ON player.teamId = team.id
// GROUP BY team.id
Team . annotated ( with : Team . players . count ) annotated(withRequired: association) and annotated(withOptional: association) extends the selection with Associations.
// SELECT player.*, team.color
// FROM player
// JOIN team ON team.id = player.teamId
Player . annotated ( withRequired : Player . team . select ( colorColumn ) ) distinct() performs uniquing.
// SELECT DISTINCT name FROM player
Player . select ( nameColumn , as : String . self ) . distinct ( ) filter(expression) applies conditions.
// SELECT * FROM player WHERE id IN (1, 2, 3)
Player . filter ( [ 1 , 2 , 3 ] . contains ( idColumn ) )
// SELECT * FROM player WHERE (name IS NOT NULL) AND (height > 1.75)
Player . filter ( nameColumn != nil && heightColumn > 1.75 ) filter(id:) and filter(ids:) are type-safe methods available on Identifiable Records:
// SELECT * FROM player WHERE id = 1
Player . filter ( id : 1 )
// SELECT * FROM country WHERE isoCode IN ('FR', 'US')
Country . filter ( ids : [ " FR " , " US " ] ) filter(key:) and filter(keys:) apply conditions on primary and unique keys:
// SELECT * FROM player WHERE id = 1
Player . filter ( key : 1 )
// SELECT * FROM country WHERE isoCode IN ('FR', 'US')
Country . filter ( keys : [ " FR " , " US " ] )
// SELECT * FROM citizenship WHERE citizenId = 1 AND countryCode = 'FR'
Citizenship . filter ( key : [ " citizenId " : 1 , " countryCode " : " FR " ] )
// SELECT * FROM player WHERE email = '[email protected]'
Player . filter ( key : [ " email " : " [email protected] " ] ) matching(pattern) (FTS3, FTS5) performs full-text search.
// SELECT * FROM document WHERE document MATCH 'sqlite database'
let pattern = FTS3Pattern ( matchingAllTokensIn : " SQLite database " )
Document . matching ( pattern )When the pattern is nil, no row will match.
group(expression, ...) groups rows.
// SELECT name, MAX(score) FROM player GROUP BY name
Player
. select ( nameColumn , max ( scoreColumn ) )
. group ( nameColumn ) having(expression) applies conditions on grouped rows.
// SELECT team, MAX(score) FROM player GROUP BY team HAVING MIN(score) >= 1000
Player
. select ( teamColumn , max ( scoreColumn ) )
. group ( teamColumn )
. having ( min ( scoreColumn ) >= 1000 ) having(aggregate) applies conditions on grouped rows, according to an association aggregate.
// SELECT team.*
// FROM team
// LEFT JOIN player ON player.teamId = team.id
// GROUP BY team.id
// HAVING COUNT(DISTINCT player.id) >= 5
Team . having ( Team . players . count >= 5 ) order(ordering, ...) sorts.
// SELECT * FROM player ORDER BY name
Player . order ( nameColumn )
// SELECT * FROM player ORDER BY score DESC, name
Player . order ( scoreColumn . desc , nameColumn ) SQLite considers NULL values to be smaller than any other values for sorting purposes. Hence, NULLs naturally appear at the beginning of an ascending ordering and at the end of a descending ordering. With a custom SQLite build, this can be changed using .ascNullsLast and .descNullsFirst :
// SELECT * FROM player ORDER BY score ASC NULLS LAST
Player . order ( nameColumn . ascNullsLast ) Each order call clears any previous ordering:
// SELECT * FROM player ORDER BY name
Player . order ( scoreColumn ) . order ( nameColumn ) reversed() reverses the eventual orderings.
// SELECT * FROM player ORDER BY score ASC, name DESC
Player . order ( scoreColumn . desc , nameColumn ) . reversed ( )If no ordering was already specified, this method has no effect:
// SELECT * FROM player
Player . all ( ) . reversed ( ) limit(limit, offset: offset) limits and pages results.
// SELECT * FROM player LIMIT 5
Player . limit ( 5 )
// SELECT * FROM player LIMIT 5 OFFSET 10
Player . limit ( 5 , offset : 10 ) joining(required:) , joining(optional:) , including(required:) , including(optional:) , and including(all:) fetch and join records through Associations.
// SELECT player.*, team.*
// FROM player
// JOIN team ON team.id = player.teamId
Player . including ( required : Player . team ) with(cte) embeds a common table expression:
// WITH ... SELECT * FROM player
let cte = CommonTableExpression ( ... )
Player . with ( cte )Other requests that involve the primary key:
selectPrimaryKey(as:) selects the primary key.
// SELECT id FROM player
Player . selectPrimaryKey ( as : Int64 . self ) // QueryInterfaceRequest<Int64>
// SELECT code FROM country
Country . selectPrimaryKey ( as : String . self ) // QueryInterfaceRequest<String>
// SELECT citizenId, countryCode FROM citizenship
Citizenship . selectPrimaryKey ( as : Row . self ) // QueryInterfaceRequest<Row> orderByPrimaryKey() sorts by primary key.
// SELECT * FROM player ORDER BY id
Player . orderByPrimaryKey ( )
// SELECT * FROM country ORDER BY code
Country . orderByPrimaryKey ( )
// SELECT * FROM citizenship ORDER BY citizenId, countryCode
Citizenship . orderByPrimaryKey ( ) groupByPrimaryKey() groups rows by primary key.
You can refine requests by chaining those methods:
// SELECT * FROM player WHERE (email IS NOT NULL) ORDER BY name
Player . order ( nameColumn ) . filter ( emailColumn != nil ) The select , order , group , and limit methods ignore and replace previously applied selection, orderings, grouping, and limits. On the opposite, filter , matching , and having methods extend the query:
Player // SELECT * FROM player
. filter ( nameColumn != nil ) // WHERE (name IS NOT NULL)
. filter ( emailColumn != nil ) // AND (email IS NOT NULL)
. order ( nameColumn ) // - ignored -
. reversed ( ) // - ignored -
. order ( scoreColumn ) // ORDER BY score
. limit ( 20 , offset : 40 ) // - ignored -
. limit ( 10 ) // LIMIT 10Raw SQL snippets are also accepted, with eventual arguments:
// SELECT DATE(creationDate), COUNT(*) FROM player WHERE name = 'Arthur' GROUP BY date(creationDate)
Player
. select ( sql : " DATE(creationDate), COUNT(*) " )
. filter ( sql : " name = ? " , arguments : [ " Arthur " ] )
. group ( sql : " DATE(creationDate) " )By default, query interface requests select all columns:
// SELECT * FROM player
struct Player : TableRecord { ... }
let request = Player . all ( )
// SELECT * FROM player
let table = Table ( " player " )
let request = table . all ( )The selection can be changed for each individual requests, or in the case of record-based requests, for all requests built from this record type.
The select(...) and select(..., as:) methods change the selection of a single request (see Fetching from Requests for detailed information):
let request = Player . select ( max ( Column ( " score " ) ) )
let maxScore = try Int . fetchOne ( db , request ) // Int?
let request = Player . select ( max ( Column ( " score " ) ) , as : Int . self )
let maxScore = try request . fetchOne ( db ) // Int? The default selection for a record type is controlled by the databaseSelection property:
struct RestrictedPlayer : TableRecord {
static let databaseTableName = " player "
static var databaseSelection : [ any SQLSelectable ] { [ Column ( " id " ) , Column ( " name " ) ] }
}
struct ExtendedPlayer : TableRecord {
static let databaseTableName = " player "
static var databaseSelection : [ any SQLSelectable ] { [ AllColumns ( ) , Column . rowID ] }
}
// SELECT id, name FROM player
let request = RestrictedPlayer . all ( )
// SELECT *, rowid FROM player
let request = ExtendedPlayer . all ( )Note : make sure the
databaseSelectionproperty is explicitly declared as[any SQLSelectable]. If it is not, the Swift compiler may silently miss the protocol requirement, resulting in stickySELECT *requests. To verify your setup, see the How do I print a request as SQL?常问问题。
Feed requests with SQL expressions built from your Swift code:
SQLSpecificExpressible
GRDB comes with a Swift version of many SQLite built-in operators, listed below. But not all: see Embedding SQL in Query Interface Requests for a way to add support for missing SQL operators.
= , <> , < , <= , > , >= , IS , IS NOT
Comparison operators are based on the Swift operators == , != , === , !== , < , <= , > , >= :
// SELECT * FROM player WHERE (name = 'Arthur')
Player . filter ( nameColumn == " Arthur " )
// SELECT * FROM player WHERE (name IS NULL)
Player . filter ( nameColumn == nil )
// SELECT * FROM player WHERE (score IS 1000)
Player . filter ( scoreColumn === 1000 )
// SELECT * FROM rectangle WHERE width < height
Rectangle . filter ( widthColumn < heightColumn )Subqueries are supported:
// SELECT * FROM player WHERE score = (SELECT max(score) FROM player)
let maximumScore = Player . select ( max ( scoreColumn ) )
Player . filter ( scoreColumn == maximumScore )
// SELECT * FROM player WHERE score = (SELECT max(score) FROM player)
let maximumScore = SQLRequest ( " SELECT max(score) FROM player " )
Player . filter ( scoreColumn == maximumScore )Note : SQLite string comparison, by default, is case-sensitive and not Unicode-aware. See string comparison if you need more control.
* , / , + , -
SQLite arithmetic operators are derived from their Swift equivalent:
// SELECT ((temperature * 1.8) + 32) AS fahrenheit FROM planet
Planet . select ( ( temperatureColumn * 1.8 + 32 ) . forKey ( " fahrenheit " ) )Note : an expression like
nameColumn + "rrr"will be interpreted by SQLite as a numerical addition (with funny results), not as a string concatenation. See theconcatoperator below.
When you want to join a sequence of expressions with the + or * operator, use joined(operator:) :
// SELECT score + bonus + 1000 FROM player
let values = [
scoreColumn ,
bonusColumn ,
1000 . databaseValue ]
Player . select ( values . joined ( operator : . add ) ) Note in the example above how you concatenate raw values: 1000.databaseValue . A plain 1000 would not compile.
When the sequence is empty, joined(operator: .add) returns 0, and joined(operator: .multiply) returns 1.
& , | , ~ , << , >>
Bitwise operations (bitwise and, or, not, left shift, right shift) are derived from their Swift equivalent:
// SELECT mask & 2 AS isRocky FROM planet
Planet . select ( ( Column ( " mask " ) & 2 ) . forKey ( " isRocky " ) ) ||
Concatenate several strings:
// SELECT firstName || ' ' || lastName FROM player
Player . select ( [ firstNameColumn , " " . databaseValue , lastNameColumn ] . joined ( operator : . concat ) ) Note in the example above how you concatenate raw strings: " ".databaseValue . A plain " " would not compile.
When the sequence is empty, joined(operator: .concat) returns the empty string.
AND , OR , NOT
The SQL logical operators are derived from the Swift && , ||和! ：
// SELECT * FROM player WHERE ((NOT verified) OR (score < 1000))
Player . filter ( !verifiedColumn || scoreColumn < 1000 ) When you want to join a sequence of expressions with the AND or OR operator, use joined(operator:) :
// SELECT * FROM player WHERE (verified AND (score >= 1000) AND (name IS NOT NULL))
let conditions = [
verifiedColumn ,
scoreColumn >= 1000 ,
nameColumn != nil ]
Player . filter ( conditions . joined ( operator : . and ) ) When the sequence is empty, joined(operator: .and) returns true, and joined(operator: .or) returns false:
// SELECT * FROM player WHERE 1
Player . filter ( [ ] . joined ( operator : . and ) )
// SELECT * FROM player WHERE 0
Player . filter ( [ ] . joined ( operator : . or ) ) BETWEEN , IN , NOT IN
To check inclusion in a Swift sequence (array, set, range…), call the contains method:
// SELECT * FROM player WHERE id IN (1, 2, 3)
Player . filter ( [ 1 , 2 , 3 ] . contains ( idColumn ) )
// SELECT * FROM player WHERE id NOT IN (1, 2, 3)
Player . filter ( ! [ 1 , 2 , 3 ] . contains ( idColumn ) )
// SELECT * FROM player WHERE score BETWEEN 0 AND 1000
Player . filter ( ( 0 ... 1000 ) . contains ( scoreColumn ) )
// SELECT * FROM player WHERE (score >= 0) AND (score < 1000)
Player . filter ( ( 0 ..< 1000 ) . contains ( scoreColumn ) )
// SELECT * FROM player WHERE initial BETWEEN 'A' AND 'N'
Player . filter ( ( " A " ... " N " ) . contains ( initialColumn ) )
// SELECT * FROM player WHERE (initial >= 'A') AND (initial < 'N')
Player . filter ( ( " A " ..< " N " ) . contains ( initialColumn ) ) To check inclusion inside a subquery, call the contains method as well:
// SELECT * FROM player WHERE id IN (SELECT playerId FROM playerSelection)
let selectedPlayerIds = PlayerSelection . select ( playerIdColumn )
Player . filter ( selectedPlayerIds . contains ( idColumn ) )
// SELECT * FROM player WHERE id IN (SELECT playerId FROM playerSelection)
let selectedPlayerIds = SQLRequest ( " SELECT playerId FROM playerSelection " )
Player . filter ( selectedPlayerIds . contains ( idColumn ) ) To check inclusion inside a common table expression, call the contains method as well:
// WITH selectedName AS (...)
// SELECT * FROM player WHERE name IN selectedName
let cte = CommonTableExpression ( named : " selectedName " , ... )
Player
. with ( cte )
. filter ( cte . contains ( nameColumn ) )Note : SQLite string comparison, by default, is case-sensitive and not Unicode-aware. See string comparison if you need more control.
EXISTS , NOT EXISTS
To check if a subquery would return rows, call the exists method:
// Teams that have at least one other player
//
// SELECT * FROM team
// WHERE EXISTS (SELECT * FROM player WHERE teamID = team.id)
let teamAlias = TableAlias ( )
let player = Player . filter ( Column ( " teamID " ) == teamAlias [ Column ( " id " ) ] )
let teams = Team . aliased ( teamAlias ) . filter ( player . exists ( ) )
// Teams that have no player
//
// SELECT * FROM team
// WHERE NOT EXISTS (SELECT * FROM player WHERE teamID = team.id)
let teams = Team . aliased ( teamAlias ) . filter ( !player . exists ( ) ) In the above example, you use a TableAlias in order to let a subquery refer to a column from another table.
In the next example, which involves the same table twice, the table alias requires an explicit disambiguation with TableAlias(name:) :
// Players who coach at least one other player
//
// SELECT coach.* FROM player coach
// WHERE EXISTS (SELECT * FROM player WHERE coachId = coach.id)
let coachAlias = TableAlias ( name : " coach " )
let coachedPlayer = Player . filter ( Column ( " coachId " ) == coachAlias [ Column ( " id " ) ] )
let coaches = Player . aliased ( coachAlias ) . filter ( coachedPlayer . exists ( ) )Finally, subqueries can also be expressed as SQL, with SQL Interpolation:
// SELECT coach.* FROM player coach
// WHERE EXISTS (SELECT * FROM player WHERE coachId = coach.id)
let coachedPlayer = SQLRequest ( " SELECT * FROM player WHERE coachId = ( coachAlias [ Column ( " id " ) ] ) " )
let coaches = Player . aliased ( coachAlias ) . filter ( coachedPlayer . exists ( ) ) LIKE
The SQLite LIKE operator is available as the like method:
// SELECT * FROM player WHERE (email LIKE '%@example.com')
Player . filter ( emailColumn . like ( " %@example.com " ) )
// SELECT * FROM book WHERE (title LIKE '%10%%' ESCAPE '')
Player . filter ( emailColumn . like ( " %10 \ %% " , escape : " \ " ) )Note : the SQLite LIKE operator is case-insensitive but not Unicode-aware. For example, the expression
'a' LIKE 'A'is true but'æ' LIKE 'Æ'is false.
MATCH
The full-text MATCH operator is available through FTS3Pattern (for FTS3 and FTS4 tables) and FTS5Pattern (for FTS5):
FTS3 and FTS4:
let pattern = FTS3Pattern ( matchingAllTokensIn : " SQLite database " )
// SELECT * FROM document WHERE document MATCH 'sqlite database'
Document . matching ( pattern )
// SELECT * FROM document WHERE content MATCH 'sqlite database'
Document . filter ( contentColumn . match ( pattern ) )FTS5:
let pattern = FTS5Pattern ( matchingAllTokensIn : " SQLite database " )
// SELECT * FROM document WHERE document MATCH 'sqlite database'
Document . matching ( pattern ) AS
To give an alias to an expression, use the forKey method:
// SELECT (score + bonus) AS total
// FROM player
Player . select ( ( Column ( " score " ) + Column ( " bonus " ) ) . forKey ( " total " ) )If you need to refer to this aliased column in another place of the request, use a detached column:
// SELECT (score + bonus) AS total
// FROM player
// ORDER BY total
Player
. select ( ( Column ( " score " ) + Column ( " bonus " ) ) . forKey ( " total " ) )
. order ( Column ( " total " ) . detached ) Unlike Column("total") , the detached column Column("total").detached is never associated to the "player" table, so it is always rendered as total in the generated SQL, even when the request involves other tables via an association or a common table expression.
SQLSpecificExpressible
GRDB comes with a Swift version of many SQLite built-in functions, listed below. But not all: see Embedding SQL in Query Interface Requests for a way to add support for missing SQL functions.
ABS , AVG , COALESCE , COUNT , DATETIME , JULIANDAY , LENGTH , MAX , MIN , SUM , TOTAL :
Those are based on the abs , average , coalesce , count , dateTime , julianDay , length , max , min , sum , and total Swift functions:
// SELECT MIN(score), MAX(score) FROM player
Player . select ( min ( scoreColumn ) , max ( scoreColumn ) )
// SELECT COUNT(name) FROM player
Player . select ( count ( nameColumn ) )
// SELECT COUNT(DISTINCT name) FROM player
Player . select ( count ( distinct : nameColumn ) )
// SELECT JULIANDAY(date, 'start of year') FROM game
Game . select ( julianDay ( dateColumn , . startOfYear ) ) For more information about the functions dateTime and julianDay , see Date And Time Functions.
CAST
Use the cast Swift function:
// SELECT (CAST(wins AS REAL) / games) AS successRate FROM player
Player . select ( ( cast ( winsColumn , as : . real ) / gamesColumn ) . forKey ( " successRate " ) )See CAST expressions for more information about SQLite conversions.
IFNULL
Use the Swift ??操作员：
// SELECT IFNULL(name, 'Anonymous') FROM player
Player . select ( nameColumn ?? " Anonymous " )
// SELECT IFNULL(name, email) FROM player
Player . select ( nameColumn ?? emailColumn ) LOWER , UPPER
The query interface does not give access to those SQLite functions. Nothing against them, but they are not unicode aware.
Instead, GRDB extends SQLite with SQL functions that call the Swift built-in string functions capitalized , lowercased , uppercased , localizedCapitalized , localizedLowercased and localizedUppercased :
Player . select ( nameColumn . uppercased ( ) )Note : When comparing strings, you'd rather use a collation:
let name : String = ... // Not recommended nameColumn . uppercased ( ) == name . uppercased ( ) // Better nameColumn . collating ( . caseInsensitiveCompare ) == name
Custom SQL functions and aggregates
You can apply your own custom SQL functions and aggregates:
let f = DatabaseFunction ( " f " , ... )
// SELECT f(name) FROM player
Player . select ( f . apply ( nameColumn ) ) You will sometimes want to extend your query interface requests with SQL snippets. This can happen because GRDB does not provide a Swift interface for some SQL function or operator, or because you want to use an SQLite construct that GRDB does not support.
Support for extensibility is large, but not unlimited. All the SQL queries built by the query interface request have the shape below. If you need something else, you'll have to use raw SQL requests.
WITH ... -- 1
SELECT ... -- 2
FROM ... -- 3
JOIN ... -- 4
WHERE ... -- 5
GROUP BY ... -- 6
HAVING ... -- 7
ORDER BY ... -- 8
LIMIT ... -- 9 WITH ... : see Common Table Expressions.
SELECT ...
The selection can be provided as raw SQL:
// SELECT IFNULL(name, 'O''Brien'), score FROM player
let request = Player . select ( sql : " IFNULL(name, 'O''Brien'), score " )
// SELECT IFNULL(name, 'O''Brien'), score FROM player
let defaultName = " O'Brien "
let request = Player . select ( sql : " IFNULL(name, ?), score " , arguments : [ suffix ] )The selection can be provided with SQL Interpolation:
// SELECT IFNULL(name, 'O''Brien'), score FROM player
let defaultName = " O'Brien "
let request = Player . select ( literal : " IFNULL(name, ( defaultName ) ), score " )The selection can be provided with a mix of Swift and SQL Interpolation:
// SELECT IFNULL(name, 'O''Brien') AS displayName, score FROM player
let defaultName = " O'Brien "
let displayName : SQL = " IFNULL( ( Column ( " name " ) ) , ( defaultName ) ) AS displayName "
let request = Player . select ( displayName , Column ( " score " ) ) When the custom SQL snippet should behave as a full-fledged expression, with support for the + Swift operator, the forKey aliasing method, and all other SQL Operators, build an expression literal with the SQL.sqlExpression method:
// SELECT IFNULL(name, 'O''Brien') AS displayName, score FROM player
let defaultName = " O'Brien "
let displayName = SQL ( " IFNULL( ( Column ( " name " ) ) , ( defaultName ) ) " ) . sqlExpression
let request = Player . select ( displayName . forKey ( " displayName " ) , Column ( " score " ) ) Such expression literals allow you to build a reusable support library of SQL functions or operators that are missing from the query interface. For example, you can define a Swift date function:
func date ( _ value : some SQLSpecificExpressible ) -> SQLExpression {
SQL ( " DATE( ( value ) ) " ) . sqlExpression
}
// SELECT * FROM "player" WHERE DATE("createdAt") = '2020-01-23'
let request = Player . filter ( date ( Column ( " createdAt " ) ) == " 2020-01-23 " ) See the Query Interface Organization for more information about SQLSpecificExpressible and SQLExpression .
FROM ... : only one table is supported here. You can not customize this SQL part.
JOIN ... : joins are fully controlled by Associations. You can not customize this SQL part.
WHERE ...
The WHERE clause can be provided as raw SQL:
// SELECT * FROM player WHERE score >= 1000
let request = Player . filter ( sql : " score >= 1000 " )
// SELECT * FROM player WHERE score >= 1000
let minScore = 1000
let request = Player . filter ( sql : " score >= ? " , arguments : [ minScore ] )The WHERE clause can be provided with SQL Interpolation:
// SELECT * FROM player WHERE score >= 1000
let minScore = 1000
let request = Player . filter ( literal : " score >= ( minScore ) " )The WHERE clause can be provided with a mix of Swift and SQL Interpolation:
// SELECT * FROM player WHERE (score >= 1000) AND (team = 'red')
let minScore = 1000
let scoreCondition : SQL = " ( Column ( " score " ) ) >= ( minScore ) "
let request = Player . filter ( scoreCondition && Column ( " team " ) == " red " ) See SELECT ... above for more SQL Interpolation examples.
GROUP BY ...
The GROUP BY clause can be provided as raw SQL, SQL Interpolation, or a mix of Swift and SQL Interpolation, just as the selection and the WHERE clause (see above).
HAVING ...
The HAVING clause can be provided as raw SQL, SQL Interpolation, or a mix of Swift and SQL Interpolation, just as the selection and the WHERE clause (see above).
ORDER BY ...
The ORDER BY clause can be provided as raw SQL, SQL Interpolation, or a mix of Swift and SQL Interpolation, just as the selection and the WHERE clause (see above).
In order to support the desc and asc query interface operators, and the reversed() query interface method, you must provide your orderings as expression literals with the SQL.sqlExpression method:
// SELECT * FROM "player"
// ORDER BY (score + bonus) ASC, name DESC
let total = SQL ( " (score + bonus) " ) . sqlExpression
let request = Player
. order ( total . desc , Column ( " name " ) )
. reversed ( ) LIMIT ... : use the limit(_:offset:) method. You can not customize this SQL part.
Once you have a request, you can fetch the records at the origin of the request:
// Some request based on `Player`
let request = Player . filter ( ... ) ... // QueryInterfaceRequest<Player>
// Fetch players:
try request . fetchCursor ( db ) // A Cursor of Player
try request . fetchAll ( db ) // [Player]
try request . fetchSet ( db ) // Set<Player>
try request . fetchOne ( db ) // Player?例如：
let allPlayers = try Player . fetchAll ( db ) // [Player]
let arthur = try Player . filter ( nameColumn == " Arthur " ) . fetchOne ( db ) // Player? See fetching methods for information about the fetchCursor , fetchAll , fetchSet and fetchOne methods.
You sometimes want to fetch other values .
The simplest way is to use the request as an argument to a fetching method of the desired type:
// Fetch an Int
let request = Player . select ( max ( scoreColumn ) )
let maxScore = try Int . fetchOne ( db , request ) // Int?
// Fetch a Row
let request = Player . select ( min ( scoreColumn ) , max ( scoreColumn ) )
let row = try Row . fetchOne ( db , request ) ! // Row
let minScore = row [ 0 ] as Int ?
let maxScore = row [ 1 ] as Int ?You can also change the request so that it knows the type it has to fetch:
With asRequest(of:) , useful when you use Associations:
struct BookInfo : FetchableRecord , Decodable {
var book : Book
var author : Author
}
// A request of BookInfo
let request = Book
. including ( required : Book . author )
. asRequest ( of : BookInfo . self )
let bookInfos = try dbQueue . read { db in
try request . fetchAll ( db ) // [BookInfo]
} With select(..., as:) , which is handy when you change the selection:
// A request of Int
let request = Player . select ( max ( scoreColumn ) , as : Int . self )
let maxScore = try dbQueue . read { db in
try request . fetchOne ( db ) // Int?
} Fetching records according to their primary key is a common task.
Identifiable Records can use the type-safe methods find(_:id:) , fetchOne(_:id:) , fetchAll(_:ids:) and fetchSet(_:ids:) :
try Player . find ( db , id : 1 ) // Player
try Player . fetchOne ( db , id : 1 ) // Player?
try Country . fetchAll ( db , ids : [ " FR " , " US " ] ) // [Countries] All record types can use find(_:key:) , fetchOne(_:key:) , fetchAll(_:keys:) and fetchSet(_:keys:) that apply conditions on primary and unique keys:
try Player . find ( db , key : 1 ) // Player
try Player . fetchOne ( db , key : 1 ) // Player?
try Country . fetchAll ( db , keys : [ " FR " , " US " ] ) // [Country]
try Player . fetchOne ( db , key : [ " email " : " [email protected] " ] ) // Player?
try Citizenship . fetchOne ( db , key : [ " citizenId " : 1 , " countryCode " : " FR " ] ) // Citizenship? When the table has no explicit primary key, GRDB uses the hidden rowid column:
// SELECT * FROM document WHERE rowid = 1
try Document . fetchOne ( db , key : 1 ) // Document? When you want to build a request and plan to fetch from it later , use a filter method:
let request = Player . filter ( id : 1 )
let request = Country . filter ( ids : [ " FR " , " US " ] )
let request = Player . filter ( key : [ " email " : " [email protected] " ] )
let request = Citizenship . filter ( key : [ " citizenId " : 1 , " countryCode " : " FR " ] ) You can check if a request has matching rows in the database.
// Some request based on `Player`
let request = Player . filter ( ... ) ...
// Check for player existence:
let noSuchPlayer = try request . isEmpty ( db ) // BoolYou should check for emptiness instead of counting:
// Correct
let noSuchPlayer = try request . fetchCount ( db ) == 0
// Even better
let noSuchPlayer = try request . isEmpty ( db )You can also check if a given primary or unique key exists in the database.
Identifiable Records can use the type-safe method exists(_:id:) :
try Player . exists ( db , id : 1 )
try Country . exists ( db , id : " FR " ) All record types can use exists(_:key:) that can check primary and unique keys:
try Player . exists ( db , key : 1 )
try Country . exists ( db , key : " FR " )
try Player . exists ( db , key : [ " email " : " [email protected] " ] )
try Citizenship . exists ( db , key : [ " citizenId " : 1 , " countryCode " : " FR " ] )You should check for key existence instead of fetching a record and checking for nil:
// Correct
let playerExists = try Player . fetchOne ( db , id : 1 ) != nil
// Even better
let playerExists = try Player . exists ( db , id : 1 ) Requests can count. The fetchCount() method returns the number of rows that would be returned by a fetch request:
// SELECT COUNT(*) FROM player
let count = try Player . fetchCount ( db ) // Int
// SELECT COUNT(*) FROM player WHERE email IS NOT NULL
let count = try Player . filter ( emailColumn != nil ) . fetchCount ( db )
// SELECT COUNT(DISTINCT name) FROM player
let count = try Player . select ( nameColumn ) . distinct ( ) . fetchCount ( db )
// SELECT COUNT(*) FROM (SELECT DISTINCT name, score FROM player)
let count = try Player . select ( nameColumn , scoreColumn ) . distinct ( ) . fetchCount ( db )Other aggregated values can also be selected and fetched (see SQL Functions):
let request = Player . select ( max ( scoreColumn ) )
let maxScore = try Int . fetchOne ( db , request ) // Int?
let request = Player . select ( min ( scoreColumn ) , max ( scoreColumn ) )
let row = try Row . fetchOne ( db , request ) ! // Row
let minScore = row [ 0 ] as Int ?
let maxScore = row [ 1 ] as Int ? Requests can delete records , with the deleteAll() method:
// DELETE FROM player
try Player . deleteAll ( db )
// DELETE FROM player WHERE team = 'red'
try Player
. filter ( teamColumn == " red " )
. deleteAll ( db )
// DELETE FROM player ORDER BY score LIMIT 10
try Player
. order ( scoreColumn )
. limit ( 10 )
. deleteAll ( db )Note Deletion methods are available on types that adopt the TableRecord protocol, and
Table:struct Player : TableRecord { ... } try Player . deleteAll ( db ) // Fine try Table ( " player " ) . deleteAll ( db ) // Just as fine
Deleting records according to their primary key is a common task.
Identifiable Records can use the type-safe methods deleteOne(_:id:) and deleteAll(_:ids:) :
try Player . deleteOne ( db , id : 1 )
try Country . deleteAll ( db , ids : [ " FR " , " US " ] ) All record types can use deleteOne(_:key:) and deleteAll(_:keys:) that apply conditions on primary and unique keys:
try Player . deleteOne ( db , key : 1 )
try Country . deleteAll ( db , keys : [ " FR " , " US " ] )
try Player . deleteOne ( db , key : [ " email " : " [email protected] " ] )
try Citizenship . deleteOne ( db , key : [ " citizenId " : 1 , " countryCode " : " FR " ] ) When the table has no explicit primary key, GRDB uses the hidden rowid column:
// DELETE FROM document WHERE rowid = 1
try Document . deleteOne ( db , id : 1 ) // Document? Requests can batch update records . The updateAll() method accepts column assignments defined with the set(to:) method:
// UPDATE player SET score = 0, isHealthy = 1, bonus = NULL
try Player . updateAll ( db ,
Column ( " score " ) . set ( to : 0 ) ,
Column ( " isHealthy " ) . set ( to : true ) ,
Column ( " bonus " ) . set ( to : nil ) )
// UPDATE player SET score = 0 WHERE team = 'red'
try Player
. filter ( Column ( " team " ) == " red " )
. updateAll ( db , Column ( " score " ) . set ( to : 0 ) )
// UPDATE player SET top = 1 ORDER BY score DESC LIMIT 10
try Player
. order ( Column ( " score " ) . desc )
. limit ( 10 )
. updateAll ( db , Column ( " top " ) . set ( to : true ) )
// UPDATE country SET population = 67848156 WHERE id = 'FR'
try Country
. filter ( id : " FR " )
. updateAll ( db , Column ( " population " ) . set ( to : 67_848_156 ) )Column assignments accept any expression:
// UPDATE player SET score = score + (bonus * 2)
try Player . updateAll ( db , Column ( " score " ) . set ( to : Column ( " score " ) + Column ( " bonus " ) * 2 ) ) As a convenience, you can also use the += , -= , *= , or /= operators:
// UPDATE player SET score = score + (bonus * 2)
try Player . updateAll ( db , Column ( " score " ) += Column ( " bonus " ) * 2 )Default Conflict Resolution rules apply, and you may also provide a specific one:
// UPDATE OR IGNORE player SET ...
try Player . updateAll ( db , onConflict : . ignore , /* assignments... */ )Note The
updateAllmethod is available on types that adopt the TableRecord protocol, andTable:struct Player : TableRecord { ... } try Player . updateAll ( db , ... ) // Fine try Table ( " player " ) . updateAll ( db , ... ) // Just as fine
Until now, we have seen requests created from any type that adopts the TableRecord protocol:
let request = Player . all ( ) // QueryInterfaceRequest<Player> Those requests of type QueryInterfaceRequest can fetch and count:
try request . fetchCursor ( db ) // A Cursor of Player
try request . fetchAll ( db ) // [Player]
try request . fetchSet ( db ) // Set<Player>
try request . fetchOne ( db ) // Player?
try request . fetchCount ( db ) // IntWhen the query interface can not generate the SQL you need , you can still fallback to raw SQL:
// Custom SQL is always welcome
try Player . fetchAll ( db , sql : " SELECT ... " ) // [Player]But you may prefer to bring some elegance back in, and build custom requests:
// No custom SQL in sight
try Player . customRequest ( ) . fetchAll ( db ) // [Player]To build custom requests , you can use one of the built-in requests or derive requests from other requests.
SQLRequest is a fetch request built from raw SQL.例如：
extension Player {
static func filter ( color : Color ) -> SQLRequest < Player > {
SQLRequest < Player > (
sql : " SELECT * FROM player WHERE color = ? "
arguments : [ color ] )
}
}
// [Player]
try Player . filter ( color : . red ) . fetchAll ( db )SQLRequest supports SQL Interpolation:
extension Player {
static func filter ( color : Color ) -> SQLRequest < Player > {
" SELECT * FROM player WHERE color = ( color ) "
}
} The asRequest(of:) method changes the type fetched by the request. It is useful, for example, when you use Associations:
struct BookInfo : FetchableRecord , Decodable {
var book : Book
var author : Author
}
let request = Book
. including ( required : Book . author )
. asRequest ( of : BookInfo . self )
// [BookInfo]
try request . fetchAll ( db ) The adapted(_:) method eases the consumption of complex rows with row adapters. See RowAdapter and splittingRowAdapters(columnCounts:) for a sample code that uses adapted(_:) .
GRDB can encrypt your database with SQLCipher v3.4+.
Use CocoaPods, and specify in your Podfile :
# GRDB with SQLCipher 4
pod 'GRDB.swift/SQLCipher'
pod 'SQLCipher' , '~> 4.0'
# GRDB with SQLCipher 3
pod 'GRDB.swift/SQLCipher'
pod 'SQLCipher' , '~> 3.4' Make sure you remove any existing pod 'GRDB.swift' from your Podfile. GRDB.swift/SQLCipher must be the only active GRDB pod in your whole project, or you will face linker or runtime errors, due to the conflicts between SQLCipher and the system SQLite.
You create and open an encrypted database by providing a passphrase to your database connection:
var config = Configuration ( )
config . prepareDatabase { db in
try db . usePassphrase ( " secret " )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config ) It is also in prepareDatabase that you perform other SQLCipher configuration steps that must happen early in the lifetime of a SQLCipher connection.例如：
var config = Configuration ( )
config . prepareDatabase { db in
try db . usePassphrase ( " secret " )
try db . execute ( sql : " PRAGMA cipher_page_size = ... " )
try db . execute ( sql : " PRAGMA kdf_iter = ... " )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config ) When you want to open an existing SQLCipher 3 database with SQLCipher 4, you may want to run the cipher_compatibility pragma:
// Open an SQLCipher 3 database with SQLCipher 4
var config = Configuration ( )
config . prepareDatabase { db in
try db . usePassphrase ( " secret " )
try db . execute ( sql : " PRAGMA cipher_compatibility = 3 " )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )See SQLCipher 4.0.0 Release and Upgrading to SQLCipher 4 for more information.
You can change the passphrase of an already encrypted database.
When you use a database queue, open the database with the old passphrase, and then apply the new passphrase:
try dbQueue . write { db in
try db . changePassphrase ( " newSecret " )
} When you use a database pool, make sure that no concurrent read can happen by changing the passphrase within the barrierWriteWithoutTransaction block. You must also ensure all future reads open a new database connection by calling the invalidateReadOnlyConnections method:
try dbPool . barrierWriteWithoutTransaction { db in
try db . changePassphrase ( " newSecret " )
dbPool . invalidateReadOnlyConnections ( )
}Note : When an application wants to keep on using a database queue or pool after the passphrase has changed, it is responsible for providing the correct passphrase to the
usePassphrasemethod called in the database preparation function.考虑：// WRONG: this won't work across a passphrase change let passphrase = try getPassphrase ( ) var config = Configuration ( ) config . prepareDatabase { db in try db . usePassphrase ( passphrase ) } // CORRECT: get the latest passphrase when it is needed var config = Configuration ( ) config . prepareDatabase { db in let passphrase = try getPassphrase ( ) try db . usePassphrase ( passphrase ) }
Note : The
DatabasePool.barrierWriteWithoutTransactionmethod does not prevent database snapshots from accessing the database during the passphrase change, or after the new passphrase has been applied to the database. Those database accesses may throw errors. Applications should provide their own mechanism for invalidating open snapshots before the passphrase is changed.
Note : Instead of changing the passphrase "in place" as described here, you can also export the database in a new encrypted database that uses the new passphrase. See Exporting a Database to an Encrypted Database.
Providing a passphrase won't encrypt a clear-text database that already exists, though. SQLCipher can't do that, and you will get an error instead: SQLite error 26: file is encrypted or is not a database .
Instead, create a new encrypted database, at a distinct location, and export the content of the existing database. This can both encrypt a clear-text database, or change the passphrase of an encrypted database.
The technique to do that is documented by SQLCipher.
With GRDB, it gives:
// The existing database
let existingDBQueue = try DatabaseQueue ( path : " /path/to/existing.db " )
// The new encrypted database, at some distinct location:
var config = Configuration ( )
config . prepareDatabase { db in
try db . usePassphrase ( " secret " )
}
let newDBQueue = try DatabaseQueue ( path : " /path/to/new.db " , configuration : config )
try existingDBQueue . inDatabase { db in
try db . execute (
sql : """
ATTACH DATABASE ? AS encrypted KEY ?;
SELECT sqlcipher_export('encrypted');
DETACH DATABASE encrypted;
""" ,
arguments : [ newDBQueue . path , " secret " ] )
}
// Now the export is completed, and the existing database can be deleted. It is recommended to avoid keeping the passphrase in memory longer than necessary. To do this, make sure you load the passphrase from the prepareDatabase method:
// NOT RECOMMENDED: this keeps the passphrase in memory longer than necessary
let passphrase = try getPassphrase ( )
var config = Configuration ( )
config . prepareDatabase { db in
try db . usePassphrase ( passphrase )
}
// RECOMMENDED: only load the passphrase when it is needed
var config = Configuration ( )
config . prepareDatabase { db in
let passphrase = try getPassphrase ( )
try db . usePassphrase ( passphrase )
}This technique helps manages the lifetime of the passphrase, although keep in mind that the content of a String may remain intact in memory long after the object has been released.
For even better control over the lifetime of the passphrase in memory, use a Data object which natively provides the resetBytes function.
// RECOMMENDED: only load the passphrase when it is needed and reset its content immediately after use
var config = Configuration ( )
config . prepareDatabase { db in
var passphraseData = try getPassphraseData ( ) // Data
defer {
passphraseData . resetBytes ( in : 0 ..< passphraseData . count )
}
try db . usePassphrase ( passphraseData )
}Some demanding users will want to go further, and manage the lifetime of the raw passphrase bytes.见下文。
GRDB offers convenience methods for providing the database passphrases as Swift strings: usePassphrase(_:) and changePassphrase(_:) . Those methods don't keep the passphrase String in memory longer than necessary. But they are as secure as the standard String type: the lifetime of actual passphrase bytes in memory is not under control.
When you want to precisely manage the passphrase bytes, talk directly to SQLCipher, using its raw C functions.
例如：
var config = Configuration ( )
config . prepareDatabase { db in
... // Carefully load passphrase bytes
let code = sqlite3_key ( db . sqliteConnection , /* passphrase bytes */ )
... // Carefully dispose passphrase bytes
guard code == SQLITE_OK else {
throw DatabaseError (
resultCode : ResultCode ( rawValue : code ) ,
message : db . lastErrorMessage )
}
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config ) When the passphrase is securely stored in the system keychain, your application can protect it using the kSecAttrAccessible attribute.
Such protection prevents GRDB from creating SQLite connections when the passphrase is not available:
var config = Configuration ( )
config . prepareDatabase { db in
let passphrase = try loadPassphraseFromSystemKeychain ( )
try db . usePassphrase ( passphrase )
}
// Success if and only if the passphrase is available
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )For the same reason, database pools, which open SQLite connections on demand, may fail at any time as soon as the passphrase becomes unavailable:
// Success if and only if the passphrase is available
let dbPool = try DatabasePool ( path : dbPath , configuration : config )
// May fail if passphrase has turned unavailable
try dbPool . read { ... }
// May trigger value observation failure if passphrase has turned unavailable
try dbPool . write { ... }Because DatabasePool maintains a pool of long-lived SQLite connections, some database accesses will use an existing connection, and succeed. And some other database accesses will fail, as soon as the pool wants to open a new connection. It is impossible to predict which accesses will succeed or fail.
For the same reason, a database queue, which also maintains a long-lived SQLite connection, will remain available even after the passphrase has turned unavailable.
Applications are thus responsible for protecting database accesses when the passphrase is unavailable. To this end, they can use Data Protection. They can also destroy their instances of database queue or pool when the passphrase becomes unavailable.
You can backup (copy) a database into another.
Backups can for example help you copying an in-memory database to and from a database file when you implement NSDocument subclasses.
let source : DatabaseQueue = ... // or DatabasePool
let destination : DatabaseQueue = ... // or DatabasePool
try source . backup ( to : destination ) The backup method blocks the current thread until the destination database contains the same contents as the source database.
When the source is a database pool, concurrent writes can happen during the backup. Those writes may, or may not, be reflected in the backup, but they won't trigger any error.
Database has an analogous backup method.
let source : DatabaseQueue = ... // or DatabasePool
let destination : DatabaseQueue = ... // or DatabasePool
try source . write { sourceDb in
try destination . barrierWriteWithoutTransaction { destDb in
try sourceDb . backup ( to : destDb )
}
} This method allows for the choice of source and destination Database handles with which to backup the database.
The backup methods take optional pagesPerStep and progress parameters. Together these parameters can be used to track a database backup in progress and abort an incomplete backup.
When pagesPerStep is provided, the database backup is performed in steps . At each step, no more than pagesPerStep database pages are copied from the source to the destination. The backup proceeds one step at a time until all pages have been copied.
When a progress callback is provided, progress is called after every backup step, including the last. Even if a non-default pagesPerStep is specified or the backup is otherwise completed in a single step, the progress callback will be called.
try source . backup (
to : destination ,
pagesPerStep : ... )
{ backupProgress in
print ( " Database backup progress: " , backupProgress )
} If a call to progress throws when backupProgress.isComplete == false , the backup will be aborted and the error rethrown. However, if a call to progress throws when backupProgress.isComplete == true , the backup is unaffected and the error is silently ignored.
Warning : Passing non-default values of
pagesPerSteporprogressto the backup methods is an advanced API intended to provide additional capabilities to expert users. GRDB's backup API provides a faithful, low-level wrapper to the underlying SQLite online backup API. GRDB's documentation is not a comprehensive substitute for the official SQLite documentation of their backup API.
The interrupt() method causes any pending database operation to abort and return at its earliest opportunity.
It can be called from any thread.
dbQueue . interrupt ( )
dbPool . interrupt ( ) A call to interrupt() that occurs when there are no running SQL statements is a no-op and has no effect on SQL statements that are started after interrupt() returns.
A database operation that is interrupted will throw a DatabaseError with code SQLITE_INTERRUPT . If the interrupted SQL operation is an INSERT, UPDATE, or DELETE that is inside an explicit transaction, then the entire transaction will be rolled back automatically. If the rolled back transaction was started by a transaction-wrapping method such as DatabaseWriter.write or Database.inTransaction , then all database accesses will throw a DatabaseError with code SQLITE_ABORT until the wrapping method returns.
例如：
try dbQueue . write { db in
try Player ( ... ) . insert ( db ) // throws SQLITE_INTERRUPT
try Player ( ... ) . insert ( db ) // not executed
} // throws SQLITE_INTERRUPT
try dbQueue . write { db in
do {
try Player ( ... ) . insert ( db ) // throws SQLITE_INTERRUPT
} catch { }
} // throws SQLITE_ABORT
try dbQueue . write { db in
do {
try Player ( ... ) . insert ( db ) // throws SQLITE_INTERRUPT
} catch { }
try Player ( ... ) . insert ( db ) // throws SQLITE_ABORT
} // throws SQLITE_ABORT You can catch both SQLITE_INTERRUPT and SQLITE_ABORT errors:
do {
try dbPool . write { db in ... }
} catch DatabaseError . SQLITE_INTERRUPT , DatabaseError . SQLITE_ABORT {
// Oops, the database was interrupted.
}For more information, see Interrupt A Long-Running Query.
SQL injection is a technique that lets an attacker nuke your database.
https://xkcd.com/327/
Here is an example of code that is vulnerable to SQL injection:
// BAD BAD BAD
let id = 1
let name = textField . text
try dbQueue . write { db in
try db . execute ( sql : " UPDATE students SET name = ' ( name ) ' WHERE id = ( id ) " )
} If the user enters a funny string like Robert'; DROP TABLE students; -- , SQLite will see the following SQL, and drop your database table instead of updating a name as intended:
UPDATE students SET name = ' Robert ' ;
DROP TABLE students;
-- ' WHERE id = 1To avoid those problems, never embed raw values in your SQL queries . The only correct technique is to provide arguments to your raw SQL queries:
let name = textField . text
try dbQueue . write { db in
// Good
try db . execute (
sql : " UPDATE students SET name = ? WHERE id = ? " ,
arguments : [ name , id ] )
// Just as good
try db . execute (
sql : " UPDATE students SET name = :name WHERE id = :id " ,
arguments : [ " name " : name , " id " : id ] )
}When you use records and the query interface, GRDB always prevents SQL injection for you:
let id = 1
let name = textField . text
try dbQueue . write { db in
if var student = try Student . fetchOne ( db , id : id ) {
student . name = name
try student . update ( db )
}
} GRDB can throw DatabaseError, RecordError, or crash your program with a fatal error.
Considering that a local database is not some JSON loaded from a remote server, GRDB focuses on trusted databases . Dealing with untrusted databases requires extra care.
DatabaseError
DatabaseError are thrown on SQLite errors:
do {
try Pet ( masterId : 1 , name : " Bobby " ) . insert ( db )
} catch let error as DatabaseError {
// The SQLite error code: 19 (SQLITE_CONSTRAINT)
error . resultCode
// The extended error code: 787 (SQLITE_CONSTRAINT_FOREIGNKEY)
error . extendedResultCode
// The eventual SQLite message: FOREIGN KEY constraint failed
error . message
// The eventual erroneous SQL query
// "INSERT INTO pet (masterId, name) VALUES (?, ?)"
error . sql
// The eventual SQL arguments
// [1, "Bobby"]
error . arguments
// Full error description
// > SQLite error 19: FOREIGN KEY constraint failed -
// > while executing `INSERT INTO pet (masterId, name) VALUES (?, ?)`
error . description
}If you want to see statement arguments in the error description, make statement arguments public.
SQLite uses results codes to distinguish between various errors .
You can catch a DatabaseError and match on result codes:
do {
try ...
} catch let error as DatabaseError {
switch error {
case DatabaseError . SQLITE_CONSTRAINT_FOREIGNKEY :
// foreign key constraint error
case DatabaseError . SQLITE_CONSTRAINT :
// any other constraint error
default :
// any other database error
}
}You can also directly match errors on result codes:
do {
try ...
} catch DatabaseError . SQLITE_CONSTRAINT_FOREIGNKEY {
// foreign key constraint error
} catch DatabaseError . SQLITE_CONSTRAINT {
// any other constraint error
} catch {
// any other database error
} Each DatabaseError has two codes: an extendedResultCode (see extended result code), and a less precise resultCode (see primary result code). Extended result codes are refinements of primary result codes, as SQLITE_CONSTRAINT_FOREIGNKEY is to SQLITE_CONSTRAINT , for example.
Warning : SQLite has progressively introduced extended result codes across its versions. The SQLite release notes are unfortunately not quite clear about that: write your handling of extended result codes with care.
RecordError
RecordError is thrown by the PersistableRecord protocol when the update method could not find any row to update:
do {
try player . update ( db )
} catch let RecordError . recordNotFound ( databaseTableName : table , key : key ) {
print ( " Key ( key ) was not found in table ( table ) . " )
} RecordError is also thrown by the FetchableRecord protocol when the find method does not find any record:
do {
let player = try Player . find ( db , id : 42 )
} catch let RecordError . recordNotFound ( databaseTableName : table , key : key ) {
print ( " Key ( key ) was not found in table ( table ) . " )
}Fatal errors notify that the program, or the database, has to be changed.
They uncover programmer errors, false assumptions, and prevent misuses.这里有几个例子：
The code asks for a non-optional value, when the database contains NULL:
// fatal error: could not convert NULL to String.
let name : String = row [ " name " ]Solution: fix the contents of the database, use NOT NULL constraints, or load an optional:
let name : String ? = row [ " name " ]Conversion from database value to Swift type fails:
// fatal error: could not convert "Mom’s birthday" to Date.
let date : Date = row [ " date " ]
// fatal error: could not convert "" to URL.
let url : URL = row [ " url " ]Solution: fix the contents of the database, or use DatabaseValue to handle all possible cases:
let dbValue : DatabaseValue = row [ " date " ]
if dbValue . isNull {
// Handle NULL
} else if let date = Date . fromDatabaseValue ( dbValue ) {
// Handle valid date
} else {
// Handle invalid date
}The database can't guarantee that the code does what it says:
// fatal error: table player has no unique index on column email
try Player . deleteOne ( db , key : [ " email " : " [email protected] " ] ) Solution: add a unique index to the player.email column, or use the deleteAll method to make it clear that you may delete more than one row:
try Player . filter ( Column ( " email " ) == " [email protected] " ) . deleteAll ( db )Database connections are not reentrant:
// fatal error: Database methods are not reentrant.
dbQueue . write { db in
dbQueue . write { db in
...
}
}Solution: avoid reentrancy, and instead pass a database connection along.
Let's consider the code below:
let sql = " SELECT ... "
// Some untrusted arguments for the query
let arguments : [ String : Any ] = ...
let rows = try Row . fetchCursor ( db , sql : sql , arguments : StatementArguments ( arguments ) )
while let row = try rows . next ( ) {
// Some untrusted database value:
let date : Date ? = row [ 0 ]
}It has two opportunities to throw fatal errors:
In such a situation, you can still avoid fatal errors by exposing and handling each failure point, one level down in the GRDB API:
// Untrusted arguments
if let arguments = StatementArguments ( arguments ) {
let statement = try db . makeStatement ( sql : sql )
try statement . setArguments ( arguments )
var cursor = try Row . fetchCursor ( statement )
while let row = try iterator . next ( ) {
// Untrusted database content
let dbValue : DatabaseValue = row [ 0 ]
if dbValue . isNull {
// Handle NULL
if let date = Date . fromDatabaseValue ( dbValue ) {
// Handle valid date
} else {
// Handle invalid date
}
}
} See Statement and DatabaseValue for more information.
SQLite can be configured to invoke a callback function containing an error code and a terse error message whenever anomalies occur.
This global error callback must be configured early in the lifetime of your application:
Database . logError = { ( resultCode , message ) in
NSLog ( " %@ " , " SQLite error ( resultCode ) : ( message ) " )
}Warning : Database.logError must be set before any database connection is opened. This includes the connections that your application opens with GRDB, but also connections opened by other tools, such as third-party libraries. Setting it after a connection has been opened is an SQLite misuse, and has no effect.
See The Error And Warning Log for more information.
SQLite lets you store unicode strings in the database.
However, SQLite does not provide any unicode-aware string transformations or comparisons.
The UPPER and LOWER built-in SQLite functions are not unicode-aware:
// "JéRôME"
try String . fetchOne ( db , sql : " SELECT UPPER('Jérôme') " ) GRDB extends SQLite with SQL functions that call the Swift built-in string functions capitalized , lowercased , uppercased , localizedCapitalized , localizedLowercased and localizedUppercased :
// "JÉRÔME"
let uppercased = DatabaseFunction . uppercase
try String . fetchOne ( db , sql : " SELECT ( uppercased . name ) ('Jérôme') " )Those unicode-aware string functions are also readily available in the query interface:
Player . select ( nameColumn . uppercased ) SQLite compares strings in many occasions: when you sort rows according to a string column, or when you use a comparison operator such as = and <= .
The comparison result comes from a collating function , or collation . SQLite comes with three built-in collations that do not support Unicode: binary, nocase, and rtrim.
GRDB comes with five extra collations that leverage unicode-aware comparisons based on the standard Swift String comparison functions and operators:
unicodeCompare (uses the built-in <= and == Swift operators)caseInsensitiveComparelocalizedCaseInsensitiveComparelocalizedComparelocalizedStandardCompareA collation can be applied to a table column. All comparisons involving this column will then automatically trigger the comparison function:
try db . create ( table : " player " ) { t in
// Guarantees case-insensitive email unicity
t . column ( " email " , . text ) . unique ( ) . collate ( . nocase )
// Sort names in a localized case insensitive way
t . column ( " name " , . text ) . collate ( . localizedCaseInsensitiveCompare )
}
// Players are sorted in a localized case insensitive way:
let players = try Player . order ( nameColumn ) . fetchAll ( db )Warning : SQLite requires host applications to provide the definition of any collation other than binary, nocase and rtrim. When a database file has to be shared or migrated to another SQLite library of platform (such as the Android version of your application), make sure you provide a compatible collation.
If you can't or don't want to define the comparison behavior of a column (see warning above), you can still use an explicit collation in SQL requests and in the query interface:
let collation = DatabaseCollation . localizedCaseInsensitiveCompare
let players = try Player . fetchAll ( db ,
sql : " SELECT * FROM player ORDER BY name COLLATE ( collation . name ) ) " )
let players = try Player . order ( nameColumn . collating ( collation ) ) . fetchAll ( db )You can also define your own collations :
let collation = DatabaseCollation ( " customCollation " ) { ( lhs , rhs ) -> NSComparisonResult in
// return the comparison of lhs and rhs strings.
}
// Make the collation available to a database connection
var config = Configuration ( )
config . prepareDatabase { db in
db . add ( collation : collation )
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config ) Both SQLite and GRDB use non-essential memory that help them perform better.
You can reclaim this memory with the releaseMemory method:
// Release as much memory as possible.
dbQueue . releaseMemory ( )
dbPool . releaseMemory ( )This method blocks the current thread until all current database accesses are completed, and the memory collected.
Warning : If
DatabasePool.releaseMemory()is called while a long read is performed concurrently, then no other read access will be possible until this long read has completed, and the memory has been released. If this does not suit your application needs, look for the asynchronous options below:
You can release memory in an asynchronous way as well:
// On a DatabaseQueue
dbQueue . asyncWriteWithoutTransaction { db in
db . releaseMemory ( )
}
// On a DatabasePool
dbPool . releaseMemoryEventually ( ) DatabasePool.releaseMemoryEventually() does not block the current thread, and does not prevent concurrent database accesses. In exchange for this convenience, you don't know when memory has been freed.
The iOS operating system likes applications that do not consume much memory.
Database queues and pools automatically free non-essential memory when the application receives a memory warning, and when the application enters background.
You can opt out of this automatic memory management:
var config = Configuration ( )
config . automaticMemoryManagement = false
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config ) // or DatabasePoolFAQ: Opening Connections
FAQ: SQL
常见问题：一般
FAQ: Associations
FAQ: ValueObservation
FAQ: Errors
First choose a proper location for the database file. Document-based applications will let the user pick a location. Apps that use the database as a global storage will prefer the Application Support directory.
The sample code below creates or opens a database file inside its dedicated directory (a recommended practice). On the first run, a new empty database file is created. On subsequent runs, the database file already exists, so it just opens a connection:
// HOW TO create an empty database, or open an existing database file
// Create the "Application Support/MyDatabase" directory
let fileManager = FileManager . default
let appSupportURL = try fileManager . url (
for : . applicationSupportDirectory , in : . userDomainMask ,
appropriateFor : nil , create : true )
let directoryURL = appSupportURL . appendingPathComponent ( " MyDatabase " , isDirectory : true )
try fileManager . createDirectory ( at : directoryURL , withIntermediateDirectories : true )
// Open or create the database
let databaseURL = directoryURL . appendingPathComponent ( " db.sqlite " )
let dbQueue = try DatabaseQueue ( path : databaseURL . path )Open a read-only connection to your resource:
// HOW TO open a read-only connection to a database resource
// Get the path to the database resource.
if let dbPath = Bundle . main . path ( forResource : " db " , ofType : " sqlite " ) {
// If the resource exists, open a read-only connection.
// Writes are disallowed because resources can not be modified.
var config = Configuration ( )
config . readonly = true
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )
} else {
// The database resource can not be found.
// Fix your setup, or report the problem to the user.
} Database connections are automatically closed when DatabaseQueue or DatabasePool instances are deinitialized.
If the correct execution of your program depends on precise database closing, perform an explicit call to close() . This method may fail and create zombie connections, so please check its detailed documentation.
When you want to debug a request that does not deliver the expected results, you may want to print the SQL that is actually executed.
You can compile the request into a prepared Statement :
try dbQueue . read { db in
let request = Player . filter ( Column ( " email " ) == " [email protected] " )
let statement = try request . makePreparedRequest ( db ) . statement
print ( statement ) // SELECT * FROM player WHERE email = ?
print ( statement . arguments ) // ["[email protected]"]
}Another option is to setup a tracing function that prints out the executed SQL requests. For example, provide a tracing function when you connect to the database:
// Prints all SQL statements
var config = Configuration ( )
config . prepareDatabase { db in
db . trace { print ( $0 ) }
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )
try dbQueue . read { db in
// Prints "SELECT * FROM player WHERE email = ?"
let players = try Player . filter ( Column ( " email " ) == " [email protected] " ) . fetchAll ( db )
} If you want to see statement arguments such as '[email protected]' in the logged statements, make statement arguments public.
Note : the generated SQL may change between GRDB releases, without notice: don't have your application rely on any specific SQL output.
Use the trace(options:_:) method, with the .profile option:
var config = Configuration ( )
config . prepareDatabase { db in
db . trace ( options : . profile ) { event in
// Prints all SQL statements with their duration
print ( event )
// Access to detailed profiling information
if case let . profile ( statement , duration ) = event , duration > 0.5 {
print ( " Slow query: ( statement . sql ) " )
}
}
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )
try dbQueue . read { db in
let players = try Player . filter ( Column ( " email " ) == " [email protected] " ) . fetchAll ( db )
// Prints "0.003s SELECT * FROM player WHERE email = ?"
} If you want to see statement arguments such as '[email protected]' in the logged statements, make statement arguments public.
Since GRDB 1.0, all backwards compatibility guarantees of semantic versioning apply: no breaking change will happen until the next major version of the library.
There is an exception, though: experimental features , marked with the " EXPERIMENTAL " badge. Those are advanced features that are too young, or lack user feedback. They are not stabilized yet.
Those experimental features are not protected by semantic versioning, and may break between two minor releases of the library. To help them becoming stable, your feedback is greatly appreciated.
No, GRDB does not support library evolution and ABI stability. The only promise is API stability according to semantic versioning, with an exception for experimental features.
Yet, GRDB can be built with the "Build Libraries for Distribution" Xcode option ( BUILD_LIBRARY_FOR_DISTRIBUTION ), so that you can build binary frameworks at your convenience.
Let's say you have two record types, Book and Author , and you want to only fetch books that have an author, and discard anonymous books.
We start by defining the association between books and authors:
struct Book : TableRecord {
...
static let author = belongsTo ( Author . self )
}
struct Author : TableRecord {
...
}And then we can write our request and only fetch books that have an author, discarding anonymous ones:
let books : [ Book ] = try dbQueue . read { db in
// SELECT book.* FROM book
// JOIN author ON author.id = book.authorID
let request = Book . joining ( required : Book . author )
return try request . fetchAll ( db )
} Note how this request does not use the filter method. Indeed, we don't have any condition to express on any column. Instead, we just need to "require that a book can be joined to its author".
See How do I filter records and only keep those that are NOT associated to another record? below for the opposite question.
Let's say you have two record types, Book and Author , and you want to only fetch anonymous books that do not have any author.
We start by defining the association between books and authors:
struct Book : TableRecord {
...
static let author = belongsTo ( Author . self )
}
struct Author : TableRecord {
...
}And then we can write our request and only fetch anonymous books that don't have any author:
let books : [ Book ] = try dbQueue . read { db in
// SELECT book.* FROM book
// LEFT JOIN author ON author.id = book.authorID
// WHERE author.id IS NULL
let authorAlias = TableAlias ( )
let request = Book
. joining ( optional : Book . author . aliased ( authorAlias ) )
. filter ( !authorAlias . exists )
return try request . fetchAll ( db )
} This request uses a TableAlias in order to be able to filter on the eventual associated author. We make sure that the Author.primaryKey is nil, which is another way to say it does not exist: the book has no author.
See How do I filter records and only keep those that are associated to another record? above for the opposite question.
Let's say you have two record types, Book and Author , and you want to fetch all books with their author name, but not the full associated author records.
We start by defining the association between books and authors:
struct Book : Decodable , TableRecord {
...
static let author = belongsTo ( Author . self )
}
struct Author : Decodable , TableRecord {
...
enum Columns {
static let name = Column ( CodingKeys . name )
}
}And then we can write our request and the ad-hoc record that decodes it:
struct BookInfo : Decodable , FetchableRecord {
var book : Book
var authorName : String ? // nil when the book is anonymous
static func all ( ) -> QueryInterfaceRequest < BookInfo > {
// SELECT book.*, author.name AS authorName
// FROM book
// LEFT JOIN author ON author.id = book.authorID
let authorName = Author . Columns . name . forKey ( CodingKeys . authorName )
return Book
. annotated ( withOptional : Book . author . select ( authorName ) )
. asRequest ( of : BookInfo . self )
}
}
let bookInfos : [ BookInfo ] = try dbQueue . read { db in
BookInfo . all ( ) . fetchAll ( db )
} By defining the request as a static method of BookInfo, you have access to the private CodingKeys.authorName , and a compiler-checked SQL column name.
By using the annotated(withOptional:) method, you append the author name to the top-level selection that can be decoded by the ad-hoc record.
By using asRequest(of:) , you enhance the type-safety of your request.
Sometimes it looks that a ValueObservation does not notify the changes you expect.
There may be four possible reasons for this:
To answer the first two questions, look at SQL statements executed by the database. This is done when you open the database connection:
// Prints all SQL statements
var config = Configuration ( )
config . prepareDatabase { db in
db . trace { print ( " SQL: ( $0 ) " ) }
}
let dbQueue = try DatabaseQueue ( path : dbPath , configuration : config )If, after that, you are convinced that the expected changes were committed into the database, and not overwritten soon after, trace observation events:
let observation = ValueObservation
. tracking { db in ... }
. print ( ) // <- trace observation events
let cancellable = observation . start ( ... ) Look at the observation logs which start with cancel or failure : maybe the observation was cancelled by your app, or did fail with an error.
Look at the observation logs which start with value : make sure, again, that the expected value was not actually notified, then overwritten.
Finally, look at the observation logs which start with tracked region . Does the printed database region cover the expected changes?
例如：
empty : The empty region, which tracks nothing and never triggers the observation.player(*) : The full player tableplayer(id,name) : The id and name columns of the player tableplayer(id,name)[1] : The id and name columns of the row with id 1 in the player tableplayer(*),team(*) : Both the full player and team tables If you happen to use the ValueObservation.trackingConstantRegion(_:) method and see a mismatch between the tracked region and your expectation, then change the definition of your observation by using tracking(_:) . You should witness that the logs which start with tracked region now evolve in order to include the expected changes, and that you get the expected notifications.
If after all those steps (thanks you!), your observation is still failing you, please open an issue and provide a minimal reproducible example!
You may get this error when using the read and write methods of database queues and pools:
// Generic parameter 'T' could not be inferred
let string = try dbQueue . read { db in
let result = try String . fetchOne ( db , ... )
return result
}This is a limitation of the Swift compiler.
The general workaround is to explicitly declare the type of the closure result:
// General Workaround
let string = try dbQueue . read { db -> String ? in
let result = try String . fetchOne ( db , ... )
return result
}You can also, when possible, write a single-line closure:
// Single-line closure workaround:
let string = try dbQueue . read { db in
try String . fetchOne ( db , ... )
} The insert and save persistence methods can trigger a compiler error in async contexts:
var player = Player ( id : nil , name : " Arthur " )
try await dbWriter . write { db in
// Error: Mutation of captured var 'player' in concurrently-executing code
try player . insert ( db )
}
print ( player . id ) // A non-nil id When this happens, prefer the inserted and saved methods instead:
// OK
var player = Player ( id : nil , name : " Arthur " )
player = try await dbWriter . write { [ player ] db in
return try player . inserted ( db )
}
print ( player . id ) // A non-nil idThis error message is self-explanatory: do check for misspelled or non-existing column names.
However, sometimes this error only happens when an app runs on a recent operating system (iOS 14+, Big Sur+, etc.) The error does not happen with previous ones.
When this is the case, there are two possible explanations:
Maybe a column name is really misspelled or missing from the database schema.
To find it, check the SQL statement that comes with the DatabaseError.
Maybe the application is using the character " instead of the single quote ' as the delimiter for string literals in raw SQL queries. Recent versions of SQLite have learned to tell about this deviation from the SQL standard, and this is why you are seeing this error 。
For example: this is not standard SQL: UPDATE player SET name = "Arthur" .
The standard version is: UPDATE player SET name = 'Arthur' .
It just happens that old versions of SQLite used to accept the former, non-standard version. Newer versions are able to reject it with an error.
The fix is to change the SQL statements run by the application: replace " with ' in your string literals.
It may also be time to learn about statement arguments and SQL injection:
let name : String = ...
// NOT STANDARD (double quote)
try db . execute ( sql : """
UPDATE player SET name = " ( name ) "
""" )
// STANDARD, BUT STILL NOT RECOMMENDED (single quote)
try db . execute ( sql : " UPDATE player SET name = ' ( name ) ' " )
// STANDARD, AND RECOMMENDED (statement arguments)
try db . execute ( sql : " UPDATE player SET name = ? " , arguments : [ name ] )For more information, see Double-quoted String Literals Are Accepted, and Configuration.acceptsDoubleQuotedStringLiterals.
Those errors may be the sign that SQLite can't access the database due to data protection.
When your application should be able to run in the background on a locked device, it has to catch this error, and, for example, wait for UIApplicationDelegate.applicationProtectedDataDidBecomeAvailable(_:) or UIApplicationProtectedDataDidBecomeAvailable notification and retry the failed database operation.
do {
try ...
} catch DatabaseError . SQLITE_IOERR , DatabaseError . SQLITE_AUTH {
// Handle possible data protection error
}This error can also be prevented altogether by using a more relaxed file protection.
You may get the error "wrong number of statement arguments" when executing a LIKE query similar to:
let name = textField . text
let players = try dbQueue . read { db in
try Player . fetchAll ( db , sql : " SELECT * FROM player WHERE name LIKE '%?%' " , arguments : [ name ] )
} The problem lies in the '%?%' pattern.
SQLite only interprets ? as a parameter when it is a placeholder for a whole value (int, double, string, blob, null). In this incorrect query, ? is just a character in the '%?%' string: it is not a query parameter, and is not processed in any way. See https://www.sqlite.org/lang_expr.html#varparam for more information about SQLite parameters.
To fix the error, you can feed the request with the pattern itself, instead of the name:
let name = textField . text
let players : [ Player ] = try dbQueue . read { db in
let pattern = " % ( name ) % "
return try Player . fetchAll ( db , sql : " SELECT * FROM player WHERE name LIKE ? " , arguments : [ pattern ] )
}GRDB.xcworkspace : it contains GRDB-enabled playgrounds to play with.谢谢
URIs don't change: people change them.
This chapter was renamed to Embedding SQL in Query Interface Requests.
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This chapter has been renamed Record Comparison.
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Custom Value Types conform to the DatabaseValueConvertible protocol.
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This chapter was removed. See the references of DatabaseReader and DatabaseWriter.
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FTS5 is enabled by default since GRDB 6.7.0.
FetchedRecordsController has been removed in GRDB 5.
The Database Observation chapter describes the other ways to observe the database.
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This chapter was replaced with the documentation of splittingRowAdapters(columnCounts:).
See Records and the Query Interface.
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This protocol has been renamed PersistableRecord in GRDB 3.0.
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The Record class is a legacy GRDB type. Since GRDB 7, it is not recommended to define record types by subclassing the Record class.
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This protocol has been renamed FetchableRecord in GRDB 3.0.
This protocol has been renamed TableRecord in GRDB 3.0.
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This chapter has been superseded by ValueObservation and DatabaseRegionObservation.
