数据表设计如下图：

DDL文件：

  1. CREATE TABLE user (
  2.     id INT(11) NOT NULL auto_increment PRIMARY KEY,
  3.     name VARCHAR(100) NOT NULL default '',
  4.     room_id INT(11)
  5. );

  7. CREATE TABLE room (
  8.     id INT(11) NOT NULL auto_increment PRIMARY KEY,
  9.     address VARCHAR(100) NOT NULL default ''
  10. );

Room.java

  1. package com.hb3.pack_16.model;

  3. public class Room {

  5.     private Integer id; 
  6.     private String address; 
  7.     
  8.     public Room() {
  9.     }
  10.     
  11.     public Integer getId() { 
  12.         return id; 
  13.     } 
  14.     public void setId(Integer id) { 
  15.         this.id = id; 
  16.     }
  17.     public String getAddress() { 
  18.         return address; 
  19.     }
  20.     public void setAddress(String address) { 
  21.         this.address = address; 
  22.     }
  23. }

User.java

  1. package com.hb3.pack_16.model;

  3. public class User {

  5.     private Integer id;
  6.     private String name;
  7.     private Room room;

  9.     public User() {
  10.     }

  12.     public Integer getId() {
  13.         return id;
  14.     }
  15.     public void setId(Integer id) {
  16.         this.id = id;
  17.     }
  18.     public String getName() {
  19.         return name;
  20.     }
  21.     public void setName(String name) {
  22.         this.name = name;
  23.     }
  24.     public Room getRoom() {
  25.         return room;
  26.     }
  27.     public void setRoom(Room room) {
  28.         this.room = room;
  29.     }
  30. }

Room.hbm.xml：

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <!DOCTYPE hibernate-mapping 
  3.     PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
  4.     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

  6. <hibernate-mapping> 

  8.     <class name="com.hb3.pack_16.model.Room" table="room">
  9.     
  10.         <id name="id" column="id"> 
  11.             <generator class="native"/> 
  12.         </id> 

  14.         <property name="address" 
  15.                   column="address" 
  16.                   type="java.lang.String"/> 
  17.     </class> 

  19. </hibernate-mapping>

User.hbm.xml：

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <!DOCTYPE hibernate-mapping 
  3.     PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
  4.     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

  6. <hibernate-mapping> 

  8.     <class name="com.hb3.pack_16.model.User" table="user">
  9.     
  10.         <id name="id" column="id" type="java.lang.Integer"> 
  11.             <generator class="native"/> 
  12.         </id> 

  14.         <property name="name" column="name" type="java.lang.String"/> 
  15.         
  16.         <many-to-one name="room" 
  17.                      column="room_id" 
  18.                      class="com.hb3.pack_16.model.Room"
  19.                      cascade="all"
  20.                      outer-join="true"/>         
  21.     </class> 

  23. </hibernate-mapping>

测试代码：

  1. package com.hb3.pack_16;

  3. import java.io.IOException;
  4. import java.sql.SQLException;

  6. import org.hibernate.Session;
  7. import org.hibernate.SessionFactory;
  8. import org.hibernate.Transaction;
  9. import org.hibernate.cfg.Configuration;

  11. import com.hb3.pack_16.model.Room;
  12. import com.hb3.pack_16.model.User;


  15. public class BusinessService {

  17.     public static void main(String[] args) throws IOException, SQLException {
  18.         
  19.         Configuration config = new Configuration().configure();
  20.         SessionFactory sessionFactory = config.buildSessionFactory();      
  21.         Session session = sessionFactory.openSession();

  23.         Room room1 = new Room(); 
  24.         room1.setAddress("NTU-M8-419"); 
  25.         Room room2 = new Room(); 
  26.         room2.setAddress("NTU-G3-302"); 
  27.                 
  28.         User user1 = new User(); 
  29.         user1.setName("shenbin"); 
  30.         user1.setRoom(room1); 
  31.                 
  32.         User user2 = new User(); 
  33.         user2.setName("chenyan"); 
  34.         user2.setRoom(room1); 
  35.                 
  36.         User user3 = new User(); 
  37.         user3.setName("yangye"); 
  38.         user3.setRoom(room2); 

  40.         Transaction tx = session.beginTransaction();   
  41.         session.save(user1);
  42.         session.save(user2);
  43.         session.save(user3);    
  44.         tx.commit();

  46.         User user = (User) session.load(User.class, new Integer(1));
  47.         System.out.println(user.getName());
  48.         System.out.println(user.getRoom().getAddress());

  50.         
  51.         session.close();
  52.         sessionFactory.close();
  53.     }
  54. }

在<many-to-one>的设定中：

cascade表示操作时的级联关系。表示主控方在进行增删改操作时，被控方是否进行相关操作。

outer-join表示查询时是否使用外连接查询方式。

outer-join为true的时候，生成的查询SQL为：

Hibernate:
select user0_.id as id1_, user0_.name as name0_1_, user0_.room_id as room3_0_1_,
room1_.id as id0_, room1_.address as address1_0_ from user user0_
left outer join room room1_ on user0_.room_id=room1_.id where user0_.id=?

outer-join为false的时候，生成的查询SQL为：Hibernate:
select user0_.id as id0_, user0_.name as name0_0_, user0_.room_id as room3_0_0_
from user user0_ where user0_.id=?
Hibernate:
select room0_.id as id0_, room0_.address as address1_0_
from room room0_ where room0_.id=?

 

不过最好使用fetch属性来表示，及fetch="join"或者fetch="select"。



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