主键关联生成的关系模型: (每个员工只属于一个部门)
t_employee(id int pk fk->t_department(id), name varchar)
t_department(id int pk, name varchar)
1、主键单向关联
实体模型:
com.lrh.hibernate.Employee(int id, String name, Department department)
com.lrh.hibernate.Department(int id, String name)
配置文件:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Employee" table="t_employee">
<id name="id">
<!-- 采用foreign生成策略,Employee的主键来源Department,forgeign会取得关联对象的标识 -->
<generator class="foreign">
<!-- 指定要参照的属性 -->
<param name="property">department</param>
</generator>
</id>
<property name="name"/>
<!-- one-to-one标签的含义,表明hibernate如何加载它的关联对象,默认是根据主键加载,
constrained="true",表明当前主键上存在一个约束,当前主键(Employee的主键)还是一个外键
参照了对端的主键(Department的主键)
-->
<one-to-one name="department" constrained="true" />
</class>
</hibernate-mapping>
<!-- com.lrh.hibernate/Department.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Department" table="t_department">
<id name="id"><generator class="native"/></id>
<property name="name"/>
</class>
</hibernate-mapping>
2、主键双向关联
实体模型:
com.lrh.hibernate.Employee(int id, String name, Department department)
com.lrh.hibernate.Department(int id, String name, Employee employee)
配置文件:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Employee" table="t_employee">
<id name="id">
<!-- 指定主键生成策略为外键 -->
<generator class="foreign">
<!-- 指定要参照的属性 -->
<param name="property">department</param>
</generator>
</id>
<property name="name"/>
<!-- 使用<one-to-one>映射一对一关系。 -->
<one-to-one name="department">
</class>
</hibernate-mapping>
配置文件:
<!-- com.lrh.hibernate/Department.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Department" table="t_department">
<id name="id"><generator class="native"/></id>
<property name="name"/>
<!--
需要在Department映射文件中加入<one-to-one>标签指向employee,指示hibernate如何加载employee
默认根据主键加载
-->
<one-to-one name="employee"/>
</class>
</hibernate-mapping>