复合主键映射需要在映射配置文件中使用<composite-id>标签，该标签是指将一个类指定为相应的复合主键，它的name属性需要指定类文件中定义的属性值，并在该标签中添加<key-property>子标签。

Note：想要使用复合映射必须要将复合主键放到一个类中，也就是讲复合主键属性和其它属性分到两个类中，并将复合主键的类实现接口Serializable，该接口隶属于java.io。

复合主键的映射关系的主键是由多个列复合而成的，对应到数据表中相当的简单，如下图：

1、类文件

这里就拿上图的表来作为示例，在表中有两个字段年限和持续时间组合成为表的主键，所以分成的新类分别命名为FiscalYearPeriod和FiscalYearPeriodPK，其中FiscalYearPeriodPK类封装表的主键属性，FiscalYearPeriod类封装其它属性以及FiscalYearPeriodPK类。

1.1 FiscalYearPeriod.java

类中封装有基本的属性，并把FiscalYearPeriodPK类作为属性封装到类中，并在配置文件中配置相应的映射，如下代码：

package com.src.hibernate; import java.sql.Date; public class FiscalYearPeriod { //时间主键 private FiscalYearPeriodPK fiscalYearPeriodPK; public FiscalYearPeriodPK getFiscalYearPeriodPK() { return fiscalYearPeriodPK; } public void setFiscalYearPeriodPK(FiscalYearPeriodPK fiscalYearPeriodPK) { this.fiscalYearPeriodPK = fiscalYearPeriodPK; } //开始日期 private Date beginDate; public Date getBeginDate() { return beginDate; } public void setBeginDate(Date beginDate) { this.beginDate = beginDate; } //结束日期 private Date endDate; public Date getEndDate() { return endDate; } public void setEndDate(Date endDate) { this.endDate = endDate; } //阶段时间 private String periodSts; public String getPeriodSts() { return periodSts; } public void setPeriodSts(String periodSts) { this.periodSts = periodSts; } }

1.2 FiscalYearPeriodPK.java

封装主键属性，该类是从FiscalYearPeriod类中分离出来的，包含了基本的主键属性，并且需要实现接口Serializable，该类是要映射到配置文件中<composite-id>标签中要指定该类，代码如下：

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; } //持续时间 private int fiscalPeriod; public int getFiscalPeriod() { return fiscalPeriod; } public void setFiscalPeriod(int fiscalPeriod) { this.fiscalPeriod = fiscalPeriod; } }

2、配置文件

这里有个疑问两个类都是哪个需要添加映射文件？因为会使用<composite-id>标签，所以只需要为FiscalYearPeriod类添加映射即可，在该映射文件中添加对应复合主键标签，并在标签中添加对应的主键属性，如下代码：

<"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>

将上面的文件生成对应的数据库表，生成的sql语句如下：

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))

对应的表结构如下图：

3、数据操作

相应的映射文件配置好后，相应的数据操作就变得很简单了，首先从写入数据开始，向数据库中写入数据时会同时把两个类写入到数据库中，所以此时这两个类都必须转化为Transient状态，所以在保存时需要首先将FiscalYearPeriod对象首先保存到数据库中，然后它会自动关联复合属性，将信息保存到数据库中。

3.1 写入操作

写入的操作方法和以前的写入方法相同，需要定义两个对象，然后保存相应的对象信息到数据库中，代码如下：

public void testSave1(){ //声明会话对象 Session session=null; try{ //获取会话对象 session=HibernateUtils.getSession(); //开启会话 session.beginTransaction(); //创建复合对象 FiscalYearPeriodPK fiscalyearperiodpk=new FiscalYearPeriodPK(); fiscalyearperiodpk.setFiscalPeriod(2014); fiscalyearperiodpk.setFiscalYear(2012); //创建对象 FiscalYearPeriod fiscalyearperiod=new FiscalYearPeriod(); fiscalyearperiod.setFiscalYearPeriodPK(fiscalyearperiodpk); session.save(fiscalyearperiod); //提交会话 session.getTransaction().commit(); }catch(Exception e){ e.printStackTrace(); session.getTransaction().rollback(); }finally{ HibernateUtils.closeSession(session); } }

执行相应的测试方法，生成的SQL语句如下：

Hibernate: insert into t_fiscal_year_period_pk (beginDate, endDate, periodSts, fiscalYear, fiscalPeriod) values (?, ?, ?, ?, ?)

相应的数据库视图：

3.2 加载操作

相应的加载方法会和以前不同，因为在该表中主键是复合属性，所以需要创建一个类。在加载数据时需要创建主键对象，此时的主键就是一个对象，更需要为对象的属性赋值，这样才能获取对象，代码如下：

public void testLoad1(){ //声明会话对象 Session session=null; try{ //获取会话对象 session=HibernateUtils.getSession(); //开启会话 session.beginTransaction(); //创建复合对象 FiscalYearPeriodPK fiscalyearperiodpk=new FiscalYearPeriodPK(); fiscalyearperiodpk.setFiscalPeriod(2014); fiscalyearperiodpk.setFiscalYear(2012); FiscalYearPeriod fiscalyearperiod=(FiscalYearPeriod)session.load(FiscalYearPeriod.class,fiscalyearperiodpk); System.out.println("开始日期： "+fiscalyearperiod.getBeginDate()); //提交会话 session.getTransaction().commit(); }catch(Exception e){ e.printStackTrace(); session.getTransaction().rollback(); }finally{ HibernateUtils.closeSession(session); } }

生成的结果，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=? 开始日期： 2013-10-12

4、综合示例

一个规模较大公司的部门表(hibernate_dept_compositePK)，由所在区域(area)，部门名(name)，本部门人数(empCount),组建时间(birthday)等字段组成，我们使用所在区域和部门名做联合主键：

4.1 目标类：Department.java

public class Department { /** 把主键关联属性抽象出来单独写成一个类 */ //private String area; //private String name; /**把主键类对象作为成员变量*/ 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主键类：DepartmentPK.java

public class DepartmentPK implements Serializable { private static final long serialVersionUID = -288002855915204255L; private String area; private String name; /** * 覆盖hashCode方法(根据area和name判断) */ //@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; } /** * 覆盖equals(根据area和name判断) */ @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

<"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"> <> <> <composite-id name="departmentPK"> <> <key-property name="area" /> <key-property name="name" /> </composite-id> <> <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"> <> <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测试类：DepartmentTest.java

public class DepartmentTest extends TestCase { /** * 测试插入数据 */ public void save() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { Department dept = new Department(); /** 生成主键对象 */ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研发部"); 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); } } /** * 测试加载数据 */ public void load() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主键对象 */ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研发部"); 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); } } /** * 测试修改数据 */ public void update() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主键对象 */ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研发部"); 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); /** 生成主键对象 */ DepartmentPK deptPK2 = new DepartmentPK(); deptPK2.setArea("北京"); deptPK2.setName("研发部"); 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); } } /** * 测试删除数据 */ public void delete() { Session session = HibernateUtils.getSession(); Transaction t = session.beginTransaction(); try { /** 生成主键对象 */ DepartmentPK deptPK = new DepartmentPK(); deptPK.setArea("北京"); deptPK.setName("研发部"); Department dept=(Department)session.load(Department.class, deptPK); session.delete(dept); t.commit(); } catch (HibernateException e) { e.printStackTrace(); t.rollback(); } finally { HibernateUtils.closeSession(session); } } }