Hibernate的复合主键映射

转自http://yangfei520.blog.51cto.com/1041581/310555

 

1>.学过hibernate的都知道用<id>来配置主键生成策略，显然，它只能配置主键是单列的表，对于联合主键的情况<id>就无能为力了。今天翻到个复合主键映射的资料，觉得还是有一定价值的，就写了下来，以备后用。
    2>.hibernate处理复合主键映射是基于这样一种做法：把目标类中所有主键关联属性抽出来，单独写成一个类(我暂且叫它主键类)，目标类就只需持有主键类对象，而不必再包含各个主键属性；在映射文件中使用<composite-id>标签来配置主键对象并指出关联属性，普通属性照常配置；hibernate只会创建一张表在，并且把主键设置为主键类各属性的联合主键，存储和加载数据时，会自然的把关联对象各属性跟表中的主键字段对应起来。在这个操作过程中，它要求主键类必须是序列化的，并且要覆盖equals方法，最好覆盖hashCode方法。(我试验过了，不覆盖equals和hashCode，结果没有出现任何问题，而且从输出的sql语句看，也没有影响数据库操作，不知道它是否还有更深的含义？还希望高手给指点下)
    3>.例子。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：

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; } } 

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; } } 

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"> <!-- 联合主键 --> <!-- name指的是主键对象属性 --> <composite-id name="departmentPK"> <!-- 这里是主键关联属性 --> <key-property name="area" /> <key-property name="name" /> </composite-id> <!-- 其它属性 --> <property name="empCount" length="4" /> <property name="birthday" type="date" /> </class> </hibernate-mapping> 

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> 

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); } } } 

4.相对来说，复合主键映射用起来事很复杂的，无论是开发时还是升级时。所以，人们往往宁愿选择增加个主键字段，也不尽量不适用它。