Hibernate关系映射2——唯一外键关联

 一、唯一外键关联映射： (每个员工只属于一个部门)

唯一外键关联生成的关系模型：
t_employee(id int pk, name varchar, departmentid int fk->t_department(id))
t_department(id int pk, name varchar)

1、唯一外键单向关联

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"> 
             <generator class="native"/> 
         </id> 
         <property name="name"/> 
         <!-- 为<many-to-one>加上unique就变成了一对一 -->
         <many-to-one name="department" unique="true" column="departmentid"/> 
     </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、唯一外键双向关联

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"> 
             <generator class="native"/> 
         </id> 
         <property name="name"/> 
         <!-- <many-to-one>加上unique='true'表示一对一 -->
         <many-to-one name="department" unique="true" column="departmentid"/> 
     </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"/> 
         <!--
                                        只需要在另一端（department）加入<one-to-one>标签，但是hibernate默认按照主键加载，所以要指示hibernate按照指定列来加载
         -->
         <one-to-one name="employee" property-ref="department"/> 
     </class> 
 </hibernate-mapping>