Hibernate mant-to-one 映射，最简单示例

原文地址，http://blog.csdn.net/love_080808/article/details/3758344

因为我用到了，所以将其整理了一下，以便其他人阅读。

 

1.建立数据库表

create table room (
   id bigint not null  IDENTITY(1,1),
   address varchar(255),
   primary key (id)
)
create table users (
   id bigint not null  IDENTITY(1,1),
   name varchar(255),
   room_id bigint,
   primary key (id)
)

 

 users表示人room表示房间，多个人共有一个房间。

 

2.实体类Users.java

package com.crazyjava.vo;

public class Users implements java.io.Serializable {

	private static final long serialVersionUID = -1481433969291380841L;

	private Long id;
	private String name;
	private Room room;

	public Users() {
	}

	public Users(String name, Room room) {
		this.name = name;
		this.room = room;
	}

	public Long getId() {
		return this.id;
	}

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

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

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

	public Room getRoom() {
		return room;
	}

	public void setRoom(Room room) {
		this.room = room;
	}
}

 

3.实体类Room.java

package com.crazyjava.vo;

public class Room implements java.io.Serializable {
	private static final long serialVersionUID = 6788763073536851614L;
	private Long id;
	private String address;

	public Room() {
	}

	public Room(String address) {
		this.address = address;
	}

	public Long getId() {
		return this.id;
	}

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

	public String getAddress() {
		return this.address;
	}

	public void setAddress(String address) {
		this.address = address;
	}
}

 

4.映射文件

 

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">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.crazyjava.vo.Users" table="users" schema="dbo" catalog="bbs">
        <id name="id" type="java.lang.Long">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="name" type="java.lang.String">
            <column name="name" />
        </property>
        <many-to-one name="room"
                     column="room_id"
                     class="com.crazyjava.vo.Room"
                     cascade="all"
                     outer-join="true"/>
    </class>
</hibernate-mapping>

 

5.映射文件

Room.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">
<!-- 
    Mapping file autogenerated by MyEclipse Persistence Tools
-->
<hibernate-mapping>
    <class name="com.crazyjava.vo.Room" table="room" schema="dbo" catalog="bbs">
        <id name="id" type="java.lang.Long">
            <column name="id" />
            <generator class="native" />
        </id>
        <property name="address" type="java.lang.String">
            <column name="address" />
        </property>
    </class>
</hibernate-mapping>

 

在<many-to-one>中，cascade表示主控方（Users）进行save-update，delete等操作时，被控方（Room）是否也一并进行相关操作。设定为all表示主控方任何操作，被控方也进行操作。

在查询时，设定outer-join为true的情况下，hibernate将使用以下sql

Hibernate:
    select
        user0_.id as id0_1_,
        user0_.name as name0_1_,
        user0_.room_id as room3_0_1_,
        room1_.id as id1_0_,
        room1_.address as address1_0_ 
    from
        user user0_ 
    left outer join
        room room1_ 
            on user0_.room_id=room1_.id 
    where
        user0_.id=?

设为false执行sql

Hibernate: 
    select
        user0_.id as id0_0_,
        user0_.name as name0_0_,
        user0_.room_id as room3_0_0_ 
    from
        user user0_ 
    where
        user0_.id=?

Hibernate: 
    select
        room0_.id as id1_0_,
        room0_.address as address1_0_ 
    from
        room room0_ 
    where
        room0_.id=?