舉例講解Java的Hibernate框架中的多對一和一對多映射

作者：Eve Cole 更新時間：2025-06-30 20:00:04

多對一（Many-to-One）映射
多對一（many-to-one）關聯是最常見的關聯關係，其中一個對象可以與多個對象相關聯。例如，一個相同的地址對象可以與多個僱員的對象相關聯。

定義RDBMS表：
考慮一個情況，我們需要員工記錄存儲在EMPLOYEE表，將有以下結構：

 create table EMPLOYEE ( id INT NOT NULL auto_increment, first_name VARCHAR(20) default NULL, last_name VARCHAR(20) default NULL, salary INT default NULL, address INT NOT NULL, PRIMARY KEY (id));

此外，許多員工都可以有相同的地址，所以這種關聯可以使用許多一對一的關聯呈現。我們將存儲地址相關的信息在一個單獨的表，該表具有以下結構：

 create table ADDRESS ( id INT NOT NULL auto_increment, street_name VARCHAR(40) default NULL, city_name VARCHAR(40) default NULL, state_name VARCHAR(40) default NULL, zipcode VARCHAR(10) default NULL, PRIMARY KEY (id));

同時創建RBDMS表，並讓他們準備下一個實現。

定義POJO類：
讓我們實現一個POJO類員工將被用於保存與EMPLOYEE表的對象和其地址類型的變量。

 import java.util.*;public class Employee{ private int id; private String firstName; private String lastName; private int salary; private Address address; public Employee() {} public Employee(String fname, String lname, int salary, Address address ) { this.firstName = fname; this.lastName = lname; this.salary = salary; this.address = address; } public int getId() { return id; } public void setId( int id ) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName( String first_name ) { this.firstName = first_name; } public String getLastName() { return lastName; } public void setLastName( String last_name ) { this.lastName = last_name; } public int getSalary() { return salary; } public void setSalary( int salary ) { this.salary = salary; } public Address getAddress() { return address; } public void setAddress( Address address ) { this.address = address; }}

我們需要定義相應的地址表，這樣地址對象可以存儲和檢索到地址表中的另一個POJO類。

 import java.util.*;public class Address{ private int id; private String street; private String city; private String state; private String zipcode; public Address() {} public Address(String street, String city, String state, String zipcode) { this.street = street; this.city = city; this.state = state; this.zipcode = zipcode; } public int getId() { return id; } public void setId( int id ) { this.id = id; } public String getStreet() { return street; } public void setStreet( String street ) { this.street = street; } public String getCity() { return city; } public void setCity( String city ) { this.city = city; } public String getState() { return state; } public void setState( String state ) { this.state = state; } public String getZipcode() { return zipcode; } public void setZipcode( String zipcode ) { this.zipcode = zipcode; } }

定義Hibernate映射文件：
開發我們的映射文件，可指示Hibernate如何定義的類映射到數據庫表。 <many-to-one>進行元素將被用來定義規則建立Employee和Address實體之間的多對一關係。

 <?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="Employee" table="EMPLOYEE"> <meta attribute="class-description"> This class contains the employee detail. </meta> <id name="id" type="int" column="id"> <generator/> </id> <property name="firstName" column="first_name" type="string"/> <property name="lastName" column="last_name" type="string"/> <property name="salary" column="salary" type="int"/> <many-to-one name="address" column="address" not-null="true"/> </class> <class name="Address" table="ADDRESS"> <meta attribute="class-description"> This class contains the address detail. </meta> <id name="id" type="int" column="id"> <generator/> </id> <property name="street" column="street_name" type="string"/> <property name="city" column="city_name" type="string"/> <property name="state" column="state_name" type="string"/> <property name="zipcode" column="zipcode" type="string"/> </class></hibernate-mapping>

應該保存的映射文件中的格式<classname>.hbm.xml。保存映射文件中的文件Employee.hbm.xml。已經熟悉了大部分的映射細節，但讓我們再次看看映射文件中的所有元素：

映射文檔是具有<hibernate-mapping>為對應於每一個類包含2個<class>元素的根元素的XML文檔。

<class>元素被用於定義數據庫表從一個Java類特定的映射。 Java類名指定使用class元素的name屬性和使用表屬性數據庫表名指定。

<id>元素映射在類中的唯一ID屬性到數據庫表的主鍵。 id元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保存了Hibernate映射類型，這種類型的映射將會從Java轉換為SQL數據類型。

id元素內<generator>元素被用來自動生成的主鍵值。將生成元素class屬性設置為原生讓Hibernate拾取無論是identity，sequence或者hilo的算法來創建主鍵根據底層數據庫的支持能力。

<property>元素用於一個Java類的屬性映射到數據庫表中的列。元素的name屬性是指屬性的類和column屬性是指在數據庫表中的列。 type屬性保存了Hibernate映射類型，這種類型的映射將會從Java轉換為SQL數據類型。

<many-to-one>進行元素是用來設置EMPLOYEE和地址的實體之間的關係。 name屬性被設置為在父類中定義的變量，在我們的情況下，它是地址。列屬性用於在父表EMPLOYEE集的列名。

最後，我們將創建應用程序類的main（）方法來運行應用程序。我們將使用這個應用程序，以節省一些employee連同的記錄他們的地址，然後我們將申請CRUD操作上的記錄。

 import java.util.*; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee { private static SessionFactory factory; public static void main(String[] args) { try{ factory = new Configuration().configure().buildSessionFactory(); }catch (Throwable ex) { System.err.println("Failed to create sessionFactory object." + ex); throw new ExceptionInInitializerError(ex); } ManageEmployee ME = new ManageEmployee(); /* Let us have one address object */ Address address = ME.addAddress("Kondapur","Hyderabad","AP","532"); /* Add employee records in the database */ Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, address); /* Add another employee record in the database */ Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, address); /* List down all the employees */ ME.listEmployees(); /* Update employee's salary records */ ME.updateEmployee(empID1, 5000); /* Delete an employee from the database */ ME.deleteEmployee(empID2); /* List down all the employees */ ME.listEmployees(); } /* Method to add an address record in the database */ public Address addAddress(String street, String city, String state, String zipcode) { Session session = factory.openSession(); Transaction tx = null; Integer addressID = null; Address address = null; try{ tx = session.beginTransaction(); address = new Address(street, city, state, zipcode); addressID = (Integer) session.save(address); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } return address; } /* Method to add an employee record in the database */ public Integer addEmployee(String fname, String lname, int salary, Address address){ Session session = factory.openSession(); Transaction tx = null; Integer employeeID = null; try{ tx = session.beginTransaction(); Employee employee = new Employee(fname, lname, salary, address); employeeID = (Integer) session.save(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } return employeeID; } /* Method to list all the employees detail */ public void listEmployees( ){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); List employees = session.createQuery("FROM Employee").list(); for (Iterator iterator = employees.iterator(); iterator.hasNext();){ Employee employee = (Employee) iterator.next(); System.out.print("First Name: " + employee.getFirstName()); System.out.print(" Last Name: " + employee.getLastName()); System.out.println(" Salary: " + employee.getSalary()); Address add = employee.getAddress(); System.out.println("Address "); System.out.println(" Street: " + add.getStreet()); System.out.println(" City: " + add.getCity()); System.out.println(" State: " + add.getState()); System.out.println(" Zipcode: " + add.getZipcode()); } tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } } /* Method to update salary for an employee */ public void updateEmployee(Integer EmployeeID, int salary ){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); Employee employee = (Employee)session.get(Employee.class, EmployeeID); employee.setSalary( salary ); session.update(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } } /* Method to delete an employee from the records */ public void deleteEmployee(Integer EmployeeID){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); Employee employee = (Employee)session.get(Employee.class, EmployeeID); session.delete(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } }}

編譯和執行：
下面是步驟來編譯並運行上述應用程序。請確保已在進行的編譯和執行之前，適當地設置PATH和CLASSPATH。

創建hibernate.cfg.xml配置文件中配置章節解釋。
創建Employee.hbm.xml映射文件，如上圖所示。
創建Employee.java源文件，如上圖所示，並編譯它。
創建Address.java源文件，如上圖所示，並編譯它。
創建ManageEmployee.java源文件，如上圖所示，並編譯它。
執行ManageEmployee二進製文件來運行程序。

在屏幕上獲得以下結果，並同時記錄會在員工和地址表創建。

 $java ManageEmployee

 .......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Address Street: Kondapur City: Hyderabad State: AP Zipcode: 532First Name: Dilip Last Name: Kumar Salary: 3000Address Street: Kondapur City: Hyderabad State: AP Zipcode: 532First Name: Manoj Last Name: Kumar Salary: 5000Address Street: Kondapur City: Hyderabad State: AP Zipcode: 532

如果檢查員工和地址表，就應該記錄下了：

 mysql> select * from EMPLOYEE;

 +----+------------+-----------+--------+---------+| id | first_name | last_name | salary | address |+----+------------+-----------+--------+---------+| 1 | Manoj | Kumar | 5000 | 5 |+----+------------+-----------+--------+---------+1 row in set (0.00 sec)

 mysql> select * from ADDRESS;

 +----+-------------+-----------+------------+---------+| id | street_name | city_name | state_name | zipcode |+----+-------------+-----------+------------+---------+| 1 | Kondapur | Hyderabad | AP | 532 |+----+-------------+-----------+------------+---------+1 row in set (0.00 sec)

一對多（One-to-Many）映射
一對多的映射可以使用一組Java集合不包含任何重複的元素來實現。我們已經看到瞭如何設置映射集合在Hibernate中，所以如果你已經學會了集合（Set）映射，那麼所有設置可用於一對多的映射。

集合被映射到與映射表中<set>元素，並java.util.HashSet中初始化。您可以使用Set集合在類中，有一個集合中不需要重複的元素。
RDBMS表與POJO類我們依然採用上面例子中定義好的，
定義Hibernate映射文件：
讓我們指示Hibernate如何定義的類映射到數據庫表的映射文件。

 <?xml version="1.0" encoding="utf-8"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="Employee" table="EMPLOYEE"> <meta attribute="class-description"> This class contains the employee detail. </meta> <id name="id" type="int" column="id"> <generator/> </id> <set name="certificates" cascade="all"> <key column="employee_id"/> <one-to-many/> </set> <property name="firstName" column="first_name" type="string"/> <property name="lastName" column="last_name" type="string"/> <property name="salary" column="salary" type="int"/> </class> <class name="Certificate" table="CERTIFICATE"> <meta attribute="class-description"> This class contains the certificate records. </meta> <id name="id" type="int" column="id"> <generator/> </id> <property name="name" column="certificate_name" type="string"/> </class></hibernate-mapping>

應該保存的映射文件中的格式<classname>.hbm.xml。我們保存映射文件中的文件Employee.hbm.xml。你已經熟悉了大部分的映射細節，但讓我們再次看看映射文件中的所有元素：

映射文檔是具有<hibernate-mapping>為對應於每一個類包含2個<class>元素的根元素的XML文檔。

<class>元素被用於定義數據庫表從一個Java類特定的映射。 Java類名指定使用class元素的name屬性和使用表屬性數據庫表名指定。

id元素內的<generator>元素被用來自動生成的主鍵值。將生成元素的class屬性設置為原生讓Hibernate拾取identity，sequence或者hilo中的算法來創建主鍵根據底層數據庫的支持能力。

<set>元素設置證書和Employee類之間的關係。我們使用cascade屬性中<set>元素來告訴Hibernate來保存證書的對象，同時為Employee對象。 name屬性被設置為在父類中定義的變量集，在我們的例子是證書。對於每一組變量，我們需要定義在映射文件中單獨的一組元素。

<key>元素是包含外鍵的父對象，即在證書表中的列。表EMPLOYEE。

<one-to-many>元素表示一個Employee對象涉及到很多證書的對象。

創建應用程序類：
最後，我們將創建應用程序類的main（）方法來運行應用程序。我們將使用這個應用程序，以節省一些員工連同記錄證書，然後我們將應用上CRUD操作記錄。

 import java.util.*; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.Transaction;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;public class ManageEmployee { private static SessionFactory factory; public static void main(String[] args) { try{ factory = new Configuration().configure().buildSessionFactory(); }catch (Throwable ex) { System.err.println("Failed to create sessionFactory object." + ex); throw new ExceptionInInitializerError(ex); } ManageEmployee ME = new ManageEmployee(); /* Let us have a set of certificates for the first employee */ HashSet set1 = new HashSet(); set1.add(new Certificate("MCA")); set1.add(new Certificate("MBA")); set1.add(new Certificate("PMP")); /* Add employee records in the database */ Integer empID1 = ME.addEmployee("Manoj", "Kumar", 4000, set1); /* Another set of certificates for the second employee */ HashSet set2 = new HashSet(); set2.add(new Certificate("BCA")); set2.add(new Certificate("BA")); /* Add another employee record in the database */ Integer empID2 = ME.addEmployee("Dilip", "Kumar", 3000, set2); /* List down all the employees */ ME.listEmployees(); /* Update employee's salary records */ ME.updateEmployee(empID1, 5000); /* Delete an employee from the database */ ME.deleteEmployee(empID2); /* List down all the employees */ ME.listEmployees(); } /* Method to add an employee record in the database */ public Integer addEmployee(String fname, String lname, int salary, Set cert){ Session session = factory.openSession(); Transaction tx = null; Integer employeeID = null; try{ tx = session.beginTransaction(); Employee employee = new Employee(fname, lname, salary); employee.setCertificates(cert); employeeID = (Integer) session.save(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } return employeeID; } /* Method to list all the employees detail */ public void listEmployees( ){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); List employees = session.createQuery("FROM Employee").list(); for (Iterator iterator1 = employees.iterator(); iterator1.hasNext();){ Employee employee = (Employee) iterator1.next(); System.out.print("First Name: " + employee.getFirstName()); System.out.print(" Last Name: " + employee.getLastName()); System.out.println(" Salary: " + employee.getSalary()); Set certificates = employee.getCertificates(); for (Iterator iterator2 = certificates.iterator(); iterator2.hasNext();){ Certificate certName = (Certificate) iterator2.next(); System.out.println("Certificate: " + certName.getName()); } } tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } } /* Method to update salary for an employee */ public void updateEmployee(Integer EmployeeID, int salary ){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); Employee employee = (Employee)session.get(Employee.class, EmployeeID); employee.setSalary( salary ); session.update(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } } /* Method to delete an employee from the records */ public void deleteEmployee(Integer EmployeeID){ Session session = factory.openSession(); Transaction tx = null; try{ tx = session.beginTransaction(); Employee employee = (Employee)session.get(Employee.class, EmployeeID); session.delete(employee); tx.commit(); }catch (HibernateException e) { if (tx!=null) tx.rollback(); e.printStackTrace(); }finally { session.close(); } }}

編譯和執行：

 $java ManageEmployee

 .......VARIOUS LOG MESSAGES WILL DISPLAY HERE........First Name: Manoj Last Name: Kumar Salary: 4000Certificate: MBACertificate: PMPCertificate: MCAFirst Name: Dilip Last Name: Kumar Salary: 3000Certificate: BCACertificate: BAFirst Name: Manoj Last Name: Kumar Salary: 5000Certificate: MBACertificate: PMPCertificate: MCA

如果檢查員工和證書表，就應該記錄下了：

 mysql> select * from employee;

 +----+------------+-----------+--------+| id | first_name | last_name | salary |+----+------------+-----------+--------+| 1 | Manoj | Kumar | 5000 |+----+------------+-----------+--------+1 row in set (0.00 sec)

 mysql> select * from certificate;

 +----+------------------+-------------+| id | certificate_name | employee_id |+----+------------------+-------------+| 1 | MBA | 1 || 2 | PMP | 1 || 3 | MCA | 1 |+----+------------------+-------------+3 rows in set (0.00 sec)