Java乔晓松-Hibernate继承映射

l 继承映射

对象模型(Java类结构)

一个类继承体系一张表(subclass)(映射文件)

<class name="Employee" table="employee" discriminator-value="0">

<id name="id">

<generator class="native"/>

</id>

<discriminator column="type" type="int"/>

<property name="name"/>

<many-to-one name=”depart” column=”depart_id”/>

<subclass name="Skiller" discriminator-value="1">

<property name=”skill”/>

</subclass>

<subclass name="Sales" discriminator-value="2">

<property name="sell"/>

</subclass>

</class>

每个子类一张表(joined-subclass) (映射文件)

<class name="Employee" table="employee">

<id name="id">

<generator class="native"/>

</id>

<property name="name"/>

<joined-subclass name="Skiller" table="skiller">

<key column="employee_id"/>

<property name="skill"/>

</joined-subclass>

<joined-subclass name="Sales" table="sales">

<key column="employee_id"/>

<property name="sell"/>

</joined-subclass>

</class>

混合使用“一个类继承体系一张表”和“每个子类一张表” (映射文件)

<class name="Employee" table="employee">

<id name="id">

<generator class="native"/>

</id>

<discriminator column="type"/>

<property name="name"/>

<subclass name="Skiller">

<property name="net"/>

</subclass>

<subclass name=”Sales”">

<join table="sales">

<key column="employee_id"/>

<property name="sell"/>

</join>

</subclass>

</class>

每个具体类一张表(union-subclass) (映射文件)

<class name="Employee" abstract="true">

<id name="id">

<generator class="hilo"/>

</id>

<property name="name"/>

<union-subclass name="Skiller" table="skiller">

<property name="skill"/>

</union-subclass>

<union-subclass name="Sales" table="sales">

<property name="sell"/>

</union-subclass>

</class>

主健不能是identity类型，如果父类是abstract=”true”就不会有表与之对应。

隐式多态，映射文件没有联系，限制比较多很少使用。