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:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Employee" table="t_employee">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<!-- <set>映射集合,在多对多关系中,Hibernate将生成中间表 -->
<set name="departments" table="t_employee_department">
<!-- <key>指定引用至自身的外键表(t_employee_department)中的外键 -->
<key column="employeeid"/>
<!-- <many-to-many>映射多对多关系,column指定另一端在表t_employee_department中的列 -->
<many-to-many class="com.lrh.hibernate.Department" column="departmentid"/>
</set>
</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、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:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<class name="com.lrh.hibernate.Employee" table="t_employee">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<!-- <set>映射集合,在多对多关系中,Hibernate将生成第三张表 -->
<set name="departments" table="t_employee_department">
<!-- <key>指定引用至自身的外键表(t_employee_department)中的外键 -->
<key column="employeeid"/>
<!-- <many-to-many>映射多对多关系,column指定另一端在表t_employee_department中的列 -->
<many-to-many class="com.lrh.hibernate.Department" column="departmentid"/>
</set>
</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"/>
<!-- <set>映射集合,在多对多关系中,Hibernate将生成第三张表 -->
<set name="employees" table="t_employee_department">
<!-- <key>指定引用至自身的外键表(t_employee_department)中的外键 -->
<key column="department"/>
<!-- <many-to-many>映射多对多关系,column指定另一端在表t_employee_department中的列 -->
<many-to-many class="com.lrh.hibernate.Employee" column="employeeid"/>
</set>
</class>
</hibernate-mapping>