心得7-hibernate级联之多对多转换为多对一的问题剖析

   这里与多对多不同的是借用了一个中间类StudentCourse来达到把多对多的问题转换为多对一的问题，下面来举例具体介绍：

 

  先看看三个最重要的xxx.hbm.xml文件内部信息

Student.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

      "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping package="com.hbsi.many2manyTOone2many">

 

    <class name="Student" table="s">

        <id name="id">

           <generator class="native"/>

        </id>

        <property name="name" column="name"/>

        

        <set name="sc" table="s_c" inverse="true">

          <key column="s_id"/>

          <one-to-many class="StudentCourse"/>

        </set>

    </class>

    

</hibernate-mapping>

 

Course.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

      "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping package="com.hbsi.many2manyTOone2many">

 

    <class name="Course" table="c">

        <id name="id">

           <generator class="native"/>

        </id>

        <property name="name" column="name"/>

        

        <set name="sc" table="s_c" inverse="true">

          <key column="c_id"/>

          <one-to-many class="StudentCourse"/>

        </set>

    </class>

    

</hibernate-mapping>

 

StudentCourse.hbm.xml

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC

      "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

          "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping package="com.hbsi.many2manyTOone2many">

 

    <class name="StudentCourse" table="s_c">

        <id name="id">

           <generator class="native"/>

        </id>

        <property name="score" column="score"/>

        

<many-to-one name="s" column="s_id" cascade="save-update"/>

<many-to-one name="c" column="c_id" cascade="save-update"/>

 

    </class>

    

</hibernate-mapping>

 

  再看看测试文件TestApp.java

package com.hbsi.many2manyTOone2many;

 

import java.util.Set;

 

import org.hibernate.Session;

import org.junit.Test;

 

import com.hbsi.utils.HibernateSessionFactory;

 

public class TestApp {

   

   Session session = HibernateSessionFactory.getSession();

   @Test

   public void add(){

     session.beginTransaction();

     

     Student stu = new Student();

     stu.setName("keven");

     

     Course c1 = new Course();

     c1.setName("java");

     

     Course c2 = new Course();

     c2.setName("mysql");

     

     StudentCourse sc1 = new StudentCourse();

     sc1.setS(stu);

     sc1.setC(c1);

     sc1.setScore(99);

     

     session.save(sc1);

     

     StudentCourse sc2 = new StudentCourse();

     sc2.setS(stu);

     sc2.setC(c2);

     sc2.setScore(89);

     

     session.save(sc2);

     

     

     session.getTransaction().commit();

     HibernateSessionFactory.closeSession();

     

   }

   @Test

   public void find(){

      Student stu = (Student) session.get(Student.class,1);

      Set<StudentCourse> scs = stu.getSc();

      for(StudentCourse sc : scs){

        System.out.println(sc.getS().getName()+":"+sc.getC().getName()+"---"+sc.getScore());

      }

   }

}