hibernate继承映射

 

继承实现的三种策略（单表继承，具体表继承，类表继承）

 一 单表继承（例子）

<class name="Animal" table="t_animal" lazy="false">
  <id name="id">
   <generator class="native"/>
  </id>
  <discriminator column="type" type="string"/>
  <property name="name"/>
  <property name="sex"/>
  <subclass name="Pig" discriminator-value="P">
   <property name="weight"/>
  </subclass>
  <subclass name="Bird" discriminator-value="B">
   <property name="height"/>
  </subclass>
 </class>

二 具体表继承

<class name="Animal" table="t_animal">
  <id name="id">
   <generator class="native"/>
  </id>
  <property name="name"/>
  <property name="sex"/>
  <joined-subclass name="Pig" table="t_pig">
   <key column="pid"/>
   <property name="weight"/>
  </joined-subclass>
  <joined-subclass name="Bird" table="t_bird">
   <key column="bid"/>
   <property name="height"/>
  </joined-subclass>
 </class>

三 类表继承（不能用native生成ID)

 <class name="Animal" abstract="true">
  <id name="id">
   <generator class="assigned"/>
  </id>
  <property name="name"/>
  <property name="sex"/>
  <union-subclass name="Pig" table="t_pig">
   <property name="weight"/>
  </union-subclass>
  <union-subclass name="Bird" table="t_bird">
   <property name="height"/>
  </union-subclass>
 </class>