hibernate 映射组成关系

建立域模型和关系数据模型有着不同的出发点:

• 域模型: 由程序代码组成, 通过细化持久化类的的粒度可提高代码的可重用性, 简化编程
• 
• 在没有数据冗余的情况下, 应该尽可能降低表的数目, 简化表之间的參照关系, 以便提高数据的訪问速度
  
  

Hibernate 把持久化类的属性分为两种:

• 值(value)类型: 没有 OID, 不能被单独持久化, 生命周期依赖于所属的持久化类的对象的生命周期
• 实体(entity)类型: 有 OID, 能够被单独持久化, 有独立的生命周期（假设实体类型包括值类型，这个值类型就是一个组件，尽管是由两个类，不同在数据库中用同一张数据库表表示）

显然无法直接用 property 映射 pay 属性

Hibernate 使用 <component> 元素来映射组成关系, 该元素表名 pay 属性是 Worker 类一个组成部分, 在 Hibernate 中称之为组件

component

Worker.java

package com.atguigu.hibernate.entities;

public class Worker {

	private Integer id;
	private String name;

	private Pay pay;

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Pay getPay() {
		return pay;
	}

	public void setPay(Pay pay) {
		this.pay = pay;
	}

}

Worker.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">
<!-- Generated 2014-1-2 16:14:33 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="com.atguigu.hibernate.entities">
    <class name="Worker" table="WORKER">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>

        <!-- 映射组成关系 -->
        <component name="pay" class="Pay">

        	<!-- 指定组成关系的组件的属性 -->
        	<property name="monthlyPay" column="MONTHLY_PAY"></property>
        	<property name="yearPay" column="YEAR_PAY"></property>
        	<property name="vocationWithPay" column="VOCATION_WITH_PAY"></property>
        </component>

    </class>
</hibernate-mapping>

Pay.java

package com.atguigu.hibernate.entities;

public class Pay {

	private int monthlyPay;
	private int yearPay;
	private int vocationWithPay;

	public int getMonthlyPay() {
		return monthlyPay;
	}
	public void setMonthlyPay(int monthlyPay) {
		this.monthlyPay = monthlyPay;
	}
	public int getYearPay() {
		return yearPay;
	}
	public void setYearPay(int yearPay) {
		this.yearPay = yearPay;
	}
	public int getVocationWithPay() {
		return vocationWithPay;
	}
	public void setVocationWithPay(int vocationWithPay) {
		this.vocationWithPay = vocationWithPay;
	}
}

parent属性：

这里在组件中引用了父类private Worker worker;

Pay.java

package com.atguigu.hibernate.entities;

public class Pay {

	private int monthlyPay;
	private int yearPay;
	private int vocationWithPay;

	private Worker worker;

	public Worker getWorker() {
		return worker;
	}
	public void setWorker(Worker worker) {
		this.worker = worker;
	}
	public int getMonthlyPay() {
		return monthlyPay;
	}
	public void setMonthlyPay(int monthlyPay) {
		this.monthlyPay = monthlyPay;
	}
	public int getYearPay() {
		return yearPay;
	}
	public void setYearPay(int yearPay) {
		this.yearPay = yearPay;
	}
	public int getVocationWithPay() {
		return vocationWithPay;
	}
	public void setVocationWithPay(int vocationWithPay) {
		this.vocationWithPay = vocationWithPay;
	}
}

Worker.java

<?

xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 2014-1-2 16:14:33 by Hibernate Tools 3.4.0.CR1 -->
<hibernate-mapping package="com.atguigu.hibernate.entities">
    <class name="Worker" table="WORKER">
        <id name="id" type="java.lang.Integer">
            <column name="ID" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="NAME" />
        </property>

        <!-- 映射组成关系 -->
        <component name="pay" class="Pay">
        	<parent name="worker"/>
        	<!-- 指定组成关系的组件的属性 -->
        	<property name="monthlyPay" column="MONTHLY_PAY"></property>
        	<property name="yearPay" column="YEAR_PAY"></property>
        	<property name="vocationWithPay" column="VOCATION_WITH_PAY"></property>
        </component>

    </class>
</hibernate-mapping>