Hibernate ORM - 多对多双向中间实体关联关系

 

　　对于多对多的关联关系处理，前面我讲解了在数据库中建立第三张表用于维护两者的关联关系，现在我来讲解另一种比较常用且通用的处理方式，那就是将这个多对多的关联关系拆解成两个一对多的关联关系，意取从这个多对多的关联关系中提取出一个中间实体，用来表示两者的多对多关联关系，这个中间实体在数据库中存在相应的数据表映射。

 

　　一。Husband

 

package com.orm.model;

import java.util.List;

/**
 * Created by IntelliJ IDEA.
 * User: Zhong Gang
 * Date: 10/18/11
 * Time: 3:23 PM
 */
public class Husband extends DomainObject {
    private String name;

    private List<Couple> couples;

    public Husband(String name) {
        this.name = name;
    }
}

 

 

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping default-access="field">

    <class name="com.orm.model.Husband" table="husband">
        <id name="id" column="id" type="java.lang.Integer">
            <generator class="native"/>
        </id>
        <property name="name" column="name" type="java.lang.String"/>

        <bag name="couples" cascade="all">
            <key column="husbandid"/>
            <one-to-many class="com.orm.model.Couple"/>
        </bag>
    </class>

</hibernate-mapping>

 

　　二。Wife

 

package com.orm.model;

import java.util.List;

/**
 * Created by IntelliJ IDEA.
 * User: Zhong Gang
 * Date: 10/18/11
 * Time: 3:23 PM
 */
public class Wife extends DomainObject{
    private String name;

    private List<Couple> couples;

    public Wife(String name) {
        this.name = name;
    }
}

 

 

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping default-access="field">

    <class name="com.orm.model.Wife" table="wife">
        <id name="id" column="id" type="java.lang.Integer">
            <generator class="native"/>
        </id>
        <property name="name" column="name" type="java.lang.String"/>

        <bag name="couples" cascade="all">
            <key column="wifeid"/>
            <one-to-many class="com.orm.model.Couple"/>
        </bag>
    </class>

</hibernate-mapping>

 

　　三。Couple

 

package com.orm.model;

import java.util.List;

/**
 * Created by IntelliJ IDEA.
 * User: Zhong Gang
 * Date: 10/18/11
 * Time: 3:23 PM
 */
public class Couple extends DomainObject{
    private Husband husband;
    private Wife wife;

    public Couple(Husband husband, Wife wife) {
        this.husband = husband;
        this.wife = wife;
    }
}

 

 

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping default-access="field">

    <class name="com.orm.model.Couple" table="couple">
        <id name="id" column="id" type="java.lang.Integer">
            <generator class="native"/>
        </id>

        <many-to-one name="husband" class="com.orm.model.Husband" column="husbandid"/>
        <many-to-one name="wife" class="com.orm.model.Wife" column="wifeid"/>
    </class>

</hibernate-mapping>

 

　　四。测试代码

 

 

package com.orm;

import com.orm.model.Couple;
import com.orm.model.Husband;
import com.orm.model.Wife;
import com.orm.service.CoupleService;
import junit.framework.TestCase;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import java.util.ArrayList;
import java.util.List;

/**
 * Created by IntelliJ IDEA.
 * User: Zhong Gang
 * Date: 10/18/11
 * Time: 3:40 PM
 */
public class HibernateManyToManyTest extends TestCase {
    private CoupleService coupleService;

    @Override
    public void setUp() throws Exception {
        ApplicationContext context = new ClassPathXmlApplicationContext("classpath:testDataSource.xml");
        coupleService = (CoupleService) context.getBean("coupleService");
    }

    public void testManyToMany() throws Exception {
        Wife wife1 = new Wife("wife1");
        Wife wife2 = new Wife("wife2");
        coupleService.saveOrUpdate(wife1);
        coupleService.saveOrUpdate(wife2);

        Husband husband1 = new Husband("husband1");
        Husband husband2 = new Husband("husband2");
        coupleService.saveOrUpdate(husband1);
        coupleService.saveOrUpdate(husband2);

        Couple couple1 = new Couple(husband1, wife1);
        Couple couple2 = new Couple(husband1, wife2);
        Couple couple3 = new Couple(husband2, wife1);
        Couple couple4 = new Couple(husband2, wife2);
        coupleService.saveOrUpdate(couple1);
        coupleService.saveOrUpdate(couple2);
        coupleService.saveOrUpdate(couple3);
        coupleService.saveOrUpdate(couple4);
    }
}

 

　　测试结果截图

 

　　

 

　　

 

　　

 

　　最后附上源码以供参考

 

 

评论

3 楼 Wind_ZhongGang 2011-10-27  

lf6627926 写道

我把    coupleService.saveOrUpdate(wife1); 
        coupleService.saveOrUpdate(wife2); 
 
        coupleService.saveOrUpdate(husband1); 
        coupleService.saveOrUpdate(husband2); 

这四行去掉，怎么会报错呢，还有就是怎样实现查询啊！

我的事务又没有包含测试方法，所以你必须显示调用CRUD方法。
至于你的第一个问题说与直接将对象插入数据库有什么不同？我不太明白你的意思是什么？因为我的主键生成策略为native，所以如果我直接去保存couple，会因为这时主键还没有生成而报错。

2 楼 lf6627926 2011-10-26  

我把    coupleService.saveOrUpdate(wife1); 
        coupleService.saveOrUpdate(wife2); 
 
        coupleService.saveOrUpdate(husband1); 
        coupleService.saveOrUpdate(husband2); 

这四行去掉，怎么会报错呢，还有就是怎样实现查询啊！

1 楼 lf6627926 2011-10-26  

我想知道一下 ，这种与直接将对象插入数据库有什么不同呢？