接着上面的关联继续学习。

多对多的关联在数据库的逻辑上需要建立一个中间表，中间表存放其他两个表的外键。这里以User表和Goods表，中间表为Collecations。

User表字段为 username        password 

Goodsbiao表字段为goodsid    goodsname 

Collecations表字段为uname  gid     建议不要把这里的字段和上面外键字段一样。

创建pojo，User和Goods

package com.pojo;

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

public class User {
	private String username;
	private String password;
	private Set<Goods> goods = new HashSet<Goods>();

	public Set<Goods> getGoods() {
		return goods;
	}

	public void setGoods(Set<Goods> goods) {
		this.goods = goods;
	}

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}
}

package com.pojo;

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

public class Goods {
	private int goodsid;
	private String goodsname;
	private Set<User> userinfos = new HashSet<User>();

	public Set<User> getUserinfos() {
		return userinfos;
	}

	public void setUserinfos(Set<User> userinfos) {
		this.userinfos = userinfos;
	}

	public int getGoodsid() {
		return goodsid;
	}

	public void setGoodsid(int goodsid) {
		this.goodsid = goodsid;
	}

	public String getGoodsname() {
		return goodsname;
	}

	public void setGoodsname(String goodsname) {
		this.goodsname = goodsname;
	}

}

接下来写user.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>
	<!-- 一张表对应一个类    orm  -->
	<class name="com.pojo.User" table="user">
		<id column="username" name="username">
			<generator class="assigned"></generator>		
		</id>
		<property column="password" name="password"></property>
		
		<set name="goods" table="collection" cascade="all">
			<key column="uname"></key>
			<many-to-many class="com.pojo.Goods" column="gid"></many-to-many>
		</set>	
	</class>
</hibernate-mapping>

不同与一对多的set标签，这里添加了table这属性，他变了指向中间表collectations 。

cascade表示级联，相关属性请看其他的博客。

<key/>和一对多一样，这里不赘述。

<many-to-many/>class属性指向关联表，column属性指的是中间表的属性。

PS：set中的name一定要和SET<GOODS> 的对象名相同！