Java的Hibernate框架中復合主鍵映射的創建和使用教程

複合主鍵映射需要在映射配置文件中使用<composite-id>標籤，該標籤是指將一個類指定為相應的複合主鍵，它的name屬性需要指定類文件中定義的屬性值，並在該標籤中添加<key-property>子標籤。
Note：想要使用複合映射必須要將復合主鍵放到一個類中，也就是講複合主鍵屬性和其它屬性分到兩個類中，並將復合主鍵的類實現接口Serializable，該接口隸屬於java.io。
複合主鍵的映射關係的主鍵是由多個列複合而成的，對應到數據表中相當的簡單，如下圖：

1、類文件
這裡就拿上圖的表來作為示例，在表中有兩個字段年限和持續時間組合成為表的主鍵，所以分成的新類分別命名為FiscalYearPeriod和FiscalYearPeriodPK，其中FiscalYearPeriodPK類封裝表的主鍵屬性，FiscalYearPeriod類封裝其它屬性以及FiscalYearPeriodPK類。
1.1 FiscalYearPeriod.java
類中封裝有基本的屬性，並把FiscalYearPeriodPK類作為屬性封裝到類中，並在配置文件中配置相應的映射，如下代碼：

 package com.src.hibernate; import java.sql.Date; public class FiscalYearPeriod { //時間主鍵private FiscalYearPeriodPK fiscalYearPeriodPK; public FiscalYearPeriodPK getFiscalYearPeriodPK() { return fiscalYearPeriodPK; } public void setFiscalYearPeriodPK(FiscalYearPeriodPK fiscalYearPeriodPK) { this.fiscalYearPeriodPK = fiscalYearPeriodPK; } //開始日期private Date beginDate; public Date getBeginDate() { return beginDate; } public void setBeginDate(Date beginDate) { this.beginDate = beginDate; } //結束日期private Date endDate; public Date getEndDate() { return endDate; } public void setEndDate(Date endDate) { this.endDate = endDate; } //階段時間private String periodSts; public String getPeriodSts() { return periodSts; } public void setPeriodSts(String periodSts) { this.periodSts = periodSts; } }

1.2 FiscalYearPeriodPK.java
封裝主鍵屬性，該類是從FiscalYearPeriod類中分離出來的，包含了基本的主鍵屬性，並且需要實現接口Serializable，該類是要映射到配置文件中<composite-id>標籤中要指定該類，代碼如下：

 package com.src.hibernate; import java.io.Serializable; public class FiscalYearPeriodPK implements Serializable { //年限private int fiscalYear; public int getFiscalYear() { return fiscalYear; } public void setFiscalYear(int fiscalYear) { this.fiscalYear = fiscalYear; } //持續時間private int fiscalPeriod; public int getFiscalPeriod() { return fiscalPeriod; } public void setFiscalPeriod(int fiscalPeriod) { this.fiscalPeriod = fiscalPeriod; } }

2、配置文件
這裡有個疑問兩個類都是哪個需要添加映射文件？因為會使用<composite-id>標籤，所以只需要為FiscalYearPeriod類添加映射即可，在該映射文件中添加對應複合主鍵標籤，並在標籤中添加對應的主鍵屬性，如下代碼：

 <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.src.hibernate.FiscalYearPeriod" table="t_fiscal_year_period_pk"> <composite-id name="fiscalYearPeriodPK"> <key-property name="fiscalYear"></key-property> <key-property name="fiscalPeriod"></key-property> </composite-id> <property name="beginDate" type="date"/> <property name="endDate" type="date"/> <property name="periodSts"/> </class> </hibernate-mapping>

將上面的文件生成對應的數據庫表，生成的sql語句如下：

 drop table if exists t_fiscal_year_period_pk create table t_fiscal_year_period_pk (fiscalYear integer not null, fiscalPeriod integer not null, beginDate date, endDate date, periodSts varchar(255), primary key (fiscalYear, fiscalPeriod))

對應的表結構如下圖：

3、數據操作
相應的映射文件配置好後，相應的數據操作就變得很簡單了，首先從寫入數據開始，向數據庫中寫入數據時會同時把兩個類寫入到數據庫中，所以此時這兩個類都必須轉化為Transient狀態，所以在保存時需要首先將FiscalYearPeriod對象首先保存到數據庫中，然後它會自動關聯複合屬性，將信息保存到數據庫中。
3.1 寫入操作
寫入的操作方法和以前的寫入方法相同，需要定義兩個對象，然後保存相應的對象信息到數據庫中，代碼如下：

 public void testSave1(){ //聲明會話對象Session session=null; try{ //獲取會話對象session=HibernateUtils.getSession(); //開啟會話session.beginTransaction(); //創建複合對象FiscalYearPeriodPK fiscalyearperiodpk=new FiscalYearPeriodPK(); fiscalyearperiodpk.setFiscalPeriod(2014); fiscalyearperiodpk.setFiscalYear(2012); //創建對象FiscalYearPeriod fiscalyearperiod=new FiscalYearPeriod(); fiscalyearperiod.setFiscalYearPeriodPK(fiscalyearperiodpk); session.save(fiscalyearperiod); //提交會話session.getTransaction().commit(); }catch(Exception e){ e.printStackTrace(); session.getTransaction().rollback(); }finally{ HibernateUtils.closeSession(session); } }

執行相應的測試方法，生成的SQL語句如下：

Hibernate: insert into t_fiscal_year_period_pk (beginDate, endDate, periodSts, fiscalYear, fiscalPeriod) values (?, ?, ?, ?, ?)
相應的數據庫視圖：

3.2 加載操作
相應的加載方法會和以前不同，因為在該表中主鍵是複合屬性，所以需要創建一個類。在加載數據時需要創建主鍵對象，此時的主鍵就是一個對象，更需要為對象的屬性賦值，這樣才能獲取對象，代碼如下：

 public void testLoad1(){ //聲明會話對象Session session=null; try{ //獲取會話對象session=HibernateUtils.getSession(); //開啟會話session.beginTransaction(); //創建複合對象FiscalYearPeriodPK fiscalyearperiodpk=new FiscalYearPeriodPK(); fiscalyearperiodpk.setFiscalPeriod(2014); fiscalyearperiodpk.setFiscalYear(2012); FiscalYearPeriod fiscalyearperiod=(FiscalYearPeriod)session.load(FiscalYearPeriod.class,fiscalyearperiodpk); System.out.println("開始日期： "+fiscalyearperiod.getBeginDate()); //提交會話session.getTransaction().commit(); }catch(Exception e){ e.printStackTrace(); session.getTransaction().rollback(); }finally{ HibernateUtils.closeSession(session); } }

生成的結果，如下：

 Hibernate: select fiscalyear0_.fiscalYear as fiscalYear0_0_, fiscalyear0_.fiscalPeriod as fiscalPe2_0_0_, fiscalyear0_.beginDate as beginDate0_0_, fiscalyear0_.endDate as endDate0_0_, fiscalyear0_.periodSts as periodSts0_0_ from t_fiscal_year_period_pk fiscalyear0_ where fiscalyear0_.fiscalYear=? and fiscalyear0_.fiscalPeriod=? 開始日期： 2013-10-12

4、綜合示例
一個規模較大公司的部門表(hibernate_dept_compositePK)，由所在區域(area)，部門名(name)，本部門人數(empCount),組建時間(birthday)等字段組成，我們使用所在區域和部門名做聯合主鍵：
4.1 目標類：Department.java

 public class Department { /** 把主鍵關聯屬性抽像出來單獨寫成一個類*/ //private String area; //private String name; /**把主鍵類對像作為成員變量*/ private DepartmentPK departmentPK; private int empCount; private Date birthday; // public String getArea() { // return area; // } // // public void setArea(String area) { // this.area = area; // } // // public String getName() { // return name; // } // // public void setName(String name) { // this.name = name; // } public int getEmpCount() { return empCount; } public void setEmpCount(int empCount) { this.empCount = empCount; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public DepartmentPK getDepartmentPK() { return departmentPK; } public void setDepartmentPK(DepartmentPK departmentPK) { this.departmentPK = departmentPK; } }

4.2主鍵類：DepartmentPK.java

 public class DepartmentPK implements Serializable { private static final long serialVersionUID = -288002855915204255L; private String area; private String name; /** * 覆蓋hashCode方法(根據area和name判斷) */ //@Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((area == null) ? 0 : area.hashCode()); result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } /** * 覆蓋equals(根據area和name判斷) */ @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; final DepartmentPK other = (DepartmentPK) obj; if (area == null) { if (other.area != null) return false; } else if (!area.equals(other.area)) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } public String getArea() { return area; } public void setArea(String area) { this.area = area; } public String getName() { return name; } public void setName(String name) { this.name = name; } }

4.3 映射文件Department.hbm.xml

 <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="com.yangfei.hibernate.compositePk.entity.Department" table="hibernate_dept_compositePK"> <!-- 聯合主鍵--> <!-- name指的是主鍵對象屬性--> <composite-id name="departmentPK"> <!-- 這裡是主鍵關聯屬性--> <key-property name="area" /> <key-property name="name" /> </composite-id> <!-- 其它屬性--> <property name="empCount" length="4" /> <property name="birthday" type="date" /> </class> </hibernate-mapping>

4.4 hibernate配置文件hibernate.cfg.xml

 <?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <!-- Generated by MyEclipse Hibernate Tools. --> <hibernate-configuration> <session-factory> <property name="dialect">org.hibernate.dialect.Oracle9Dialect</property> <property name="connection.url">jdbc:oracle:thin:@127.0.0.1:1521:orcl10</property> <property name="connection.username">scott</property> <property name="connection.password">yf123</property> <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property> <property name="hibernate.show_sql">true</property> <mapping resource="com/yangfei/hibernate/compositePk/entity/Department.hbm.xml"/> </session-factory> </hibernate-configuration>

4.5測試類：DepartmentTest.java

 public class DepartmentTest extends TestCase { /** * 測試插入數據*/ public void save() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { Department dept = new Department(); /** 生成主鍵對象*/ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研發部"); dept.setDepartmentPK(deptPK); dept.setEmpCount(100); dept.setBirthday(new Date()); session.save(dept); t.commit(); } catch (HibernateException e) { e.printStackTrace(); t.rollback(); } finally { HibernateUtils.closeSession(session); } } /** * 測試加載數據*/ public void load() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主鍵對象*/ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研發部"); Department dept=(Department)session.load(Department.class, deptPK); System.out.println(dept.getDepartmentPK().getArea()+","+dept.getDepartmentPK().getName()+","+dept.getEmpCount()+","+dept.getBirthday()); } catch (HibernateException e) { e.printStackTrace(); t.rollback(); } finally { HibernateUtils.closeSession(session); } } /** * 測試修改數據*/ public void update() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主鍵對象*/ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研發部"); Department emp=(Department)session.load(Department.class, deptPK); System.out.println(emp.getDepartmentPK().getArea()+","+emp.getDepartmentPK().getName()+","+emp.getEmpCount()+","+emp.getBirthday()); emp.setEmpCount(100); session.saveOrUpdate(emp); /** 生成主鍵對象*/ DepartmentPK deptPK2 = new DepartmentPK(); deptPK2.setArea("北京"); deptPK2.setName("研發部"); Department dept=(Department)session.load(Department.class, deptPK2); System.out.println(dept.getDepartmentPK().getArea()+","+dept.getDepartmentPK().getName()+","+dept.getEmpCount()+","+dept.getBirthday()); t.commit(); } catch (HibernateException e) { e.printStackTrace(); t.rollback(); } finally { HibernateUtils.closeSession(session); } } /** * 測試刪除數據*/ public void delete() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主鍵對象*/ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研發部"); Department dept=(Department)session.load(Department.class, deptPK); session.delete(dept); t.commit(); } catch (HibernateException e) { e.printStackTrace(); t.rollback(); } finally { HibernateUtils.closeSession(session); } } }