Hibernate关系映射总结(三)

 上一章对一对多单向关联进行了小结，关联映射在一方User里进行了如下配置：

          < set  name ="seats"  table ="seat"  cascade ="all" >
              < key  column ="user_id"   />
              < one-to-many  class ="com.mp.persistence.model.Seat"   />
          </ set >

多对一单向关联也差不多，改在多方Seat的hbm.xml中加入如下关联映射代码就可以，同时需要把Seat.java里的user_id属性改为User对象，相应的把User中的Set<seat>属性去掉，数据库不用做修改。

         < many-to-one  name ="user"  column ="user_id"
                                                    class ="com.mp.persistence.model.User"  cascade ="all"   />

这章要总结多对多基于连接表双向关联，还是用第一章的例子，多个User对应多个Seat,一个人可以有多个座位，一个座位也可以有多个人。

通过cmd进入mysql，执行以下语句修改表seat，增加一连接表user_seat.

alter   table  seat  drop   column   user_id  ;

create   table  user_seat (
     user_id   char ( 32 ) ,
    seat_id  char ( 32 )
);

User.java：

package  com.mp.persistence.model;

import  java.util.Set;

public   class  User
... {

    private String        id;
    private String        name;
    private Set<Seat>    seats;

    public Set<Seat> getSeats()
    ...{
        return seats;
    }

    public void setSeats(Set<Seat> seats)
    ...{
        this.seats = seats;
    }

    public String getId()
    ...{
        return id;
    }

    public void setId(String id)
    ...{
        this.id = id;
    }

    public String getName()
    ...{
        return name;
    }

    public void setName(String name)
    ...{
        this.name = name;
    }

}

Seat.java:

package  com.mp.persistence.model;

import  java.util.Set;

public   class  Seat
... {

    private String        id;
    private String        place;
    private Set<User>    users;

    public Set<User> getUsers()
    ...{
        return users;
    }

    public void setUsers(Set<User> users)
    ...{
        this.users = users;
    }

    public String getId()
    ...{
        return id;
    }

    public void setId(String id)
    ...{
        this.id = id;
    }

    public String getPlace()
    ...{
        return place;
    }

    public void setPlace(String place)
    ...{
        this.place = place;
    }
}

User.hbm.xml:

<? 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 >
     < class  name ="com.mp.persistence.model.User"  table ="user" >
         < id  name ="id"  column ="id"  type ="java.lang.String" >
             < generator  class ="uuid"   />
         </ id >
         < property  name ="name"  column ="name"  type ="java.lang.String"   />
        
         < set  name ="seats"  table ="user_seat"  cascade ="save-update" >
             < key  column ="user_id"   />
             < many-to-many  class ="com.mp.persistence.model.Seat"  column ="seat_id"   />
         </ set >
        
     </ class >
</ hibernate-mapping >

set里的name与User.java里的seat对象属性对应，table为连接表，key column为关联表里关联user表的字段，many-to-many里的class为关联类，column 为连接表里关联类的关联字段。

Seat.hbm.xml:

<? 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 >
     < class  name ="com.mp.persistence.model.Seat"  table ="seat" >
         < id  name ="id"  column ="id"  type ="java.lang.String" >
             < generator  class ="uuid"   />
         </ id >
         < property  name ="place"  column ="place"  type ="java.lang.String"   />
        
         < set  name ="users"  table ="user_seat"  cascade ="save-update"  inverse ="true"   >
             < key  column ="seat_id"   />
             < many-to-many  class ="com.mp.persistence.model.User"  column ="user_id"   />
         </ set >
        
     </ class >
</ hibernate-mapping >

测试代码：

package  com.mp.persistence.model;

import  java.util.HashSet;
import  java.util.Set;

import  org.hibernate.Session;
import  org.hibernate.SessionFactory;
import  org.hibernate.Transaction;
import  org.hibernate.cfg.Configuration;

/** */ /**
 * 类功能描述：测试hibernate映射关系
 *
 * @author <a href="mailto:[email protected]">likun </a>
 * @version $Id: codetemplates.xml,v 1.1 2007/12/07 02:35:38 likun Exp  $
 * Create:  2008-1-3 下午01:00:21
 */
public   class  TestHibernate
... {

    public static void main(String[] args)
    ...{
        // 获得hibernate.cfg.xml配置信息    
        Configuration config = new Configuration().configure();
        // 根据 config 建立 SessionFactory       
        // SessionFactory 将用于建立 Session      
        SessionFactory sessionFactory = config.buildSessionFactory();
        
        Seat seat = new Seat();
        seat.setPlace("三排一列");
        seat.setUsers(new HashSet());
        Seat seat2 = new Seat();
        seat2.setPlace("三排二列");
        seat2.setUsers(new HashSet());
        
        User user = new User();
        user.setName("lucy");
        user.setSeats(new HashSet());
        User user2 = new User();
        user2.setName("lily");
        user2.setSeats(new HashSet());
        
        
        user.getSeats().add(seat);
        user.getSeats().add(seat2);
        seat.getUsers().add(user);
        seat2.getUsers().add(user);
        
        user2.getSeats().add(seat);
        user2.getSeats().add(seat2);
        seat.getUsers().add(user2);
        seat2.getUsers().add(user2);
        
        // 开启Session，相当于开启JDBC的Connection       
        Session session = sessionFactory.openSession();
        Transaction tx = session.beginTransaction();
        // 保存实体类至数据库中     
        session.save(user);
        session.save(user2);
        tx.commit();
        session.close();
        sessionFactory.close();
        System.out.println("操作成功！");
    }
}

右键Run as /Java Application ，控制台显示信息：

Hibernate: insert into user (name ,  id) values (? ,  ?)
Hibernate: insert into seat (place ,  id) values (? ,  ?)
Hibernate: insert into user (name ,  id) values (? ,  ?)
Hibernate: insert into seat (place ,  id) values (? ,  ?)
Hibernate: insert into user_seat (user_id ,  seat_id) values (? ,  ?)
Hibernate: insert into user_seat (user_id ,  seat_id) values (? ,  ?)
Hibernate: insert into user_seat (user_id ,  seat_id) values (? ,  ?)
Hibernate: insert into user_seat (user_id ,  seat_id) values (? ,  ?)
操作成功！

切换到cmd界面，查询结果如下：