天使 2011-10-24
一、多对一和一对多关联映射(多个员工属于同一部门)这几种关联映射后的关系模型都是一致的:
t_employee(id int pk, name varchar, departmentid int fk->t_department(id)) t_department(id int pk, name varchar)
1、多对一单向关联
实体模型:
com.lrh.hibernate.Employee(intid,Stringname,Departmentdepartment)
com.lrh.hibernate.Department(int id, String name)配置文件:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<classname="com.lrh.hibernate.Employee"table="t_employee">
<idname="id"><generatorclass="native"/></id>
<propertyname="name"/>
<!--<many-to-one>映射多对一关系。导出ddl时将自动生成一个外键-->
<many-to-onename="department"column="departmentid"/>
</class>
</hibernate-mapping><!--com.lrh.hibernate/Department.hbm.xml-->
<hibernate-mapping>
<classname="com.lrh.hibernate.Department"table="t_department">
<idname="id"><generatorclass="native"/></id>
<propertyname="name"/>
</class>
</hibernate-mapping>2、一对多单向关联(少用)
实体模型:
com.lrh.hibernate.Employee(intid,Stringname)
com.lrh.hibernate.Department(int id, String name, Set employees)配置文件:
<!--com.lrh.hibernate/Employee.hbm.xml-->
<hibernate-mapping>
<classname="com.lrh.hibernate.Employee"table="t_employee">
<idname="id"><generatorclass="native"/></id>
<propertyname="name"/>
</class>
</hibernate-mapping>
<!-- com.lrh.hibernate/Department.hbm.xml --><hibernate-mapping>
<classname="com.lrh.hibernate.Department"table="t_department">
<idname="id">
<generatorclass="native"/>
</id>
<propertyname="name"/>
<setname="employees">
<!--<key>指定引用至自身的外键表(t_employee)中的外键-->
<keycolumn="departmentid"/>
<!--<one-to-many>映射一对多关系-->
<one-to-manyclass="com.lrh.hibernate.Employee"/>
</set>
</class>
</hibernate-mapping>3、双向关联
实体模型:
com.lrh.hibernate.Employee(intid,Stringname,Departmentdepartment)
com.lrh.hibernate.Department(int id, String name, Set employees)配置文件:
<!-- com.lrh.hibernate/Employee.hbm.xml -->
<hibernate-mapping>
<classname="com.lrh.hibernate.Employee"table="t_employee">
<idname="id"><generatorclass="native"/></id>
<propertyname="name"/>
<!--<many-to-one>映射多对一关系-->
<many-to-onename="department"column="departmentid"/>
</class>
</hibernate-mapping>配置文件:
<!-- com.lrh.hibernate/Department.hbm.xml -->
<hibernate-mapping>
<classname="com.lrh.hibernate.Department"table="t_department">
<idname="id"><generatorclass="native"/></id>
<propertyname="name"/>
<!--双向关联中,为<set>加入”inverse=true”可以反转维护关系:
Hibernate将放弃从一的一端维护。也就是employee和department的关系必须使用employee维护,
操作department时Hibernate将不维护这个关系。
-->
<setname="employees">
<!--<key>指定引用至自身的外键表(t_employee)中的外键-->
<keycolumn="departmentid"/>
<!--<one-to-many>映射一对多关系-->
<one-to-manyclass="com.lrh.hibernate.Employee"/>
</set>
</class>
</hibernate-mapping>