hbm.xml中级联关系的配置方法

1.一对多

（1）两个表一对多关联（客户---订单）

customer.hbm.xml:

<id name="id" column="id" type="long">
   <generator class="increment"> <!-- 主键id的生成方式为自增 -->
   </generator>
  </id>

<set name="orders" cascade="save-update" inverse="true">
   <key column="customer_id"></key> <!-- key元素设定与所关联的持久化类对应的表的外键 -->
   <one-to-many class="com.test.Order"/>
  </set>

order.hbm.xml:

<id name="id" column="id" type="long">
   <generator class="increment"> <!-- 主键id的生成方式为自增 -->
   </generator>
  </id>
  <many-to-one name="customer" column="customer_id" class="com.test.Customer">
  </many-to-one>

 

（2）一对多自身双向关联

 <set name="childCategories" cascade="all" inverse="true" >
   <key column="category_id"></key>
   <one-to-many class="com.test.Category"/>
  </set>
<many-to-one name="parentCategory" column="category_id" class="com.test.Category"></many-to-one>

 

2.一对一(例子：学生---身份证)

根据数据库的设计分为一下两种：

(1)共用主键id

student.hbm.xml:

<id name="id" unsaved-value="null"><!--id的产生方式是uuid.hex-->
   <generator class="uuid.hex" />
  </id>

<one-to-one name="cer" class="model.Certificate"  fetch="join" cascade="all"  /><!--映射对应的身分证对象-->

certificate.hbm.ml:
  <id name="id">
   <generator class="foreign">
    <param name="property">stu</param>
   </generator>
  </id>

<one-to-one name="stu" class="model.Student" fetch="select"
   constrained="true" cascade="none"/>

 

(2)外键关联

student.hbm.xml:

<id name="id" unsaved-value="null"><!--id的产生方式是uuid.hex-->
   <generator class="uuid.hex" />
  </id>

<one-to-one name="cer" class="model.Certificate"  fetch="join" cascade="all"  /><!--映射对应的身分证对象-->

certificate.hbm.ml:

<id name="id">
   <generator class="uuid.hex" />
  </id>

<many-to-one name="stu"
   class="model.Student" 
   unique="true"
   column="stu_id"
  />  <!-- 唯一的多对一，实际也就变成一对一关系了 -->

3.多对多(学生---课程  通过选课表连接)

student.hbm.xml:

<id name="id" unsaved-value="null"><!--id的产生方式是uuid.hex-->
   <generator class="uuid.hex" />
  </id>

<set name="courses" table="student_course"
   cascade="none" inverse="true">
   <key column="stu_id" />
   
   <many-to-many class="model.Course"
    column="course_id" />
  </set>

course.hbm.xml:

<id name="id" unsaved-value="null" ><!--id的产生方式是uuid.hex-->
   <generator class="uuid.hex" />
  </id>

<set name="students" table="student_course"
   cascade="save-update">
   <key column="course_id" />
   <many-to-many class="model.Student"
    column="stu_id" />
  </set>