Hibernate3 之继承映射

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本文介绍了Hibernate中两种不同的继承映射策略：一种是父类和子类共用一张表，通过类型判别器进行区分；另一种是每个子类各自拥有一张表，主键与父类表关联。这两种策略各有优劣，适用于不同的场景。

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1. 父类和子类公用一张表：

<?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 package="com.ethan.domain">
	<class name="Employee" discriminator-value="0">
		<id name="id">
			<generator class="native"/>
		</id>
		
		<discriminator column="tyep" type="java.lang.Integer"></discriminator>
		<!-- name unique -->
		<property name="name"/>
		
		<!-- departId外键参考department表 -->
		<many-to-one name="depart" column="departId"/>		
		
		<subclass name="Skiller" discriminator-value="1">
			<property name="skill"></property>
		</subclass>
		
		<subclass name="Sales" discriminator-value="2">
			<property name="sell"></property>
		</subclass>
	</class>
</hibernate-mapping>

<?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 package="com.ethan.domain">
	<class name="Department">
		<id name="id">
			<generator class="native"></generator>
		</id>
		<!-- name unique -->
		<property name="name"/>
		<!-- 如果是delete，那么部门删除时，它下边的员工也会跟着删除 -->
		<set name="emps" inverse="true" cascade="save-update">
			<key column="departId"></key>
			<one-to-many class="Employee"/>
		</set>
	</class>
</hibernate-mapping>

2.子类各自一张表，主键参考父类主键，父类表中存放公有字段：

<?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 package="com.ethan.domain">
	<class name="Employee">
		<id name="id">
			<generator class="native"/>
		</id>
		
		<!-- <discriminator column="type" type="java.lang.Integer"></discriminator> -->
		<!-- name unique -->
		<property name="name" unique="true"/>
		
		<!-- departId外键参考department表 -->
		<many-to-one name="depart" column="departId"/>		
		
		<!-- <subclass name="Skiller" discriminator-value="1">
			<property name="skill"></property>
		</subclass>
		
		<subclass name="Sales" discriminator-value="2">
			<property name="sell"></property>
		</subclass> -->
		
		<joined-subclass name="Skiller" table="skiller">
			<key column="emp_id"/><!-- 引用的是id -->
			<property name="skill"></property>
		</joined-subclass>
		
		<joined-subclass name="Sales" table="sales">
			<key column="emp_id"/><!-- 引用的是id -->
			<property name="sell"></property>
		</joined-subclass>
		
		
	</class>
</hibernate-mapping>

Hibernate3 之 继承映射

Hibernate3 之继承映射