Hibernate关联映射4——多对多关联映射

一、多对多关联映射（每个员工拥有多个部门，每个部门也有多个员工）多对多关联映射关系使用中间表表示。导出关系模型时Hibernate将自动生成复合主键以及外键约束。

关系模型：
t_employee(id int pk, name varchar)
t_department(id int pk, name varchar)
t_employee_department(employeeid int fk->t_employee(id), departmentid int fk->t_department(id), pk(employeeid, departmentid))

1、多对多单向关联

实体模型：
com.lrh.hibernate.Employee(int id, String name, Set departments)
com.lrh.hibernate.Department(int id, String name)

配置文件：

<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、多对多双向关联

实体模型：
com.lrh.hibernate.Employee(int id, String name, Set departments)
com.lrh.hibernate.Department(int id, String name, Set employees)

配置文件：

<hibernate-mapping>
     <class name="com.lrh.hibernate.Employee" table="t_employee">
         <id name="id">
             <generator class="native"/>
         </id>
         <property name="name"/>
         
         <set name="departments" table="t_employee_department">
             
            <key column="employeeid"/>
             
            <many-to-many class="com.lrh.hibernate.Department" column="departmentid"/>
         </set>
     </class>
</hibernate-mapping>


<hibernate-mapping>
     <class name="com.lrh.hibernate.Department" table="t_department">
         <id name="id">
             <generator class="native"/>
         </id>
         <property name="name"/>
         
         <set name="employees" table="t_employee_department">
             
             <key column="department"/>
             
            <many-to-many class="com.lrh.hibernate.Employee" column="employeeid"/>
         </set>
     </class>
</hibernate-mapping>

Hibernate关联映射4——多对多关联映射

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