在前文hibernate之5.many2one单向 提到多对多关系，表结构设计是基于中间表来实现,

下面以用户与角色（多对多）为例,在Hibernate是如何操作的

表结构设计:

Student

package com.demo.model;

import java.io.UnsupportedEncodingException;
import java.util.Set;

/**学生信息
 * @author wobendiankun
 *2014-10-19 下午08:54:29
 */
public class Student {
	private int studentId ;
	private String studentName ;
	private int age;
	private Set<Certificate> certificates ;
	private User user;
	public int getStudentId() {
		return studentId;
	}
	public void setStudentId(int studentId) {
		this.studentId = studentId;
	}
	public String getStudentName() {
		return studentName;
	}
	public void setStudentName(String studentName) {
		this.studentName = studentName;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString() {
		String str="";
		if(studentName!=null){
			try {
				str=new String(studentName.getBytes("UTF-8"));
			} catch (UnsupportedEncodingException e) {
				e.printStackTrace();
			}
		}
		return "Student [studentId=" + studentId + ", studentName="
				+ str + ", age=" + age + "]";
	}
	public Set<Certificate> getCertificates() {
		return certificates;
	}
	public void setCertificates(Set<Certificate> certificates) {
		this.certificates = certificates;
	}
	public User getUser() {
		return user;
	}
	public void setUser(User user) {
		this.user = user;
	}
	
}

Role

package com.demo.model;

import java.util.Set;

/**角色信息
 * @author wobendiankun
 *2014-11-2 下午08:29:54
 */
public class Role {
	/**
	 * 角色id
	 */
	private int roleId;
	/**
	 * 角色名称
	 */
	private String roleName;
	
	
	public Role() {
	}
	
	public Role(int roleId) {
		this.roleId = roleId;
	}
	
	public Role(String roleName) {
		this.roleName = roleName;
	}

	private Set<User> users;
	public int getRoleId() {
		return roleId;
	}
	public void setRoleId(int roleId) {
		this.roleId = roleId;
	}
	public String getRoleName() {
		return roleName;
	}
	public void setRoleName(String roleName) {
		this.roleName = roleName;
	}
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
	
}

配置:

Role.hbm.xml

<?xml version="1.0"?>
<!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.demo.model.Role" table="t_role">
		<id name="roleId" column="role_id">
			<generator class="sequence">
				<param name="sequence">SEQ_T_ROLE</param>
			</generator>
		</id>
		<property name="roleName" column="role_name" />
		<set name="users" table="t_user_role" lazy="extra">
			<key column="role_id"></key>
			<many-to-many class="com.demo.model.User" column="user_id"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

<set name="users" table="t_user_role" lazy="extra">
<key column="role_id"></key>
<many-to-many class="com.demo.model.User" column="user_id"></many-to-many>
</set>

set元素的table属性::指中间表名

key元素的column属性:指表t_role在中间表中的关联字段

many-to-many元素的class属性:指set中的元素类型  ,column:User实体映射表t_user在中间表的关联字段

add:

</pre><pre name="code" class="java">@Test
<span style="white-space:pre">	</span>public void addTest() {
<span style="white-space:pre">		</span>User user1=new User("李三","111");
<span style="white-space:pre">		</span>User user2=new User("李四","111");
<span style="white-space:pre">		</span>Set<User> users=new HashSet<User>();
<span style="white-space:pre">		</span>users.add(user1);
<span style="white-space:pre">		</span>users.add(user2);
<span style="white-space:pre">		</span>
<span style="white-space:pre">		</span>Role role=new Role("开发组");
<span style="white-space:pre">		</span>role.setUsers(users);
<span style="white-space:pre">		</span>Session session = null;
<span style="white-space:pre">		</span>try {
<span style="white-space:pre">			</span>session = HibernateUtil.openSession();
<span style="white-space:pre">			</span>session.beginTransaction();
<span style="white-space:pre">			</span>session.save(user1);
<span style="white-space:pre">			</span>session.save(user2);
<span style="white-space:pre">			</span>session.save(role);
<span style="white-space:pre">			</span>session.getTransaction().commit();
<span style="white-space:pre">		</span>} catch (Exception e) {
<span style="white-space:pre">			</span>session.getTransaction().rollback();
<span style="white-space:pre">			</span>e.printStackTrace();
<span style="white-space:pre">		</span>} finally {
<span style="white-space:pre">			</span>HibernateUtil.closeSession(session);
<span style="white-space:pre">		</span>}
<span style="white-space:pre">	</span>}

发出sql:

Hibernate: insert into t_user (user_name, password, student_id, user_id) values (?, ?, ?, ?)
Hibernate: insert into t_user (user_name, password, student_id, user_id) values (?, ?, ?, ?)
Hibernate: insert into t_role (role_name, role_id) values (?, ?)
Hibernate: insert into t_user_role (role_id, user_id) values (?, ?)
Hibernate: insert into t_user_role (role_id, user_id) values (?, ?)

load

@Test
	public void loadTest(){
		Session session = null;
		try {
			session = HibernateUtil.openSession();
			session.beginTransaction();
			Role role=(Role)session.load(Role.class,2);
			System.out.println("角色名称"+role.getRoleName());
			System.out.println("users:"+role.getUsers());
			session.getTransaction().commit();
		} catch (Exception e) {
			session.getTransaction().rollback();
			e.printStackTrace();
		} finally {
			HibernateUtil.closeSession(session);
		}
	}

发出sql:

Hibernate: select role0_.role_id as role1_3_0_, role0_.role_name as role2_3_0_ from t_role role0_ where role0_.role_id=?
角色名称开发组
Hibernate: select users0_.role_id as role1_3_1_, users0_.user_id as user2_1_, user1_.user_id as user1_2_0_, user1_.user_name as user2_2_0_, user1_.password as password2_0_, user1_.student_id as student4_2_0_ from t_user_role users0_ inner join t_user user1_ on users0_.user_id=user1_.user_id where users0_.role_id=?
users:[com.demo.model.User@b4be3d, com.demo.model.User@35bb0f]

hibernate之 10.many2many单向