多对多关联映射（双向关联）见项目：me_many_to_many

1.模型
一个用户拥有多个角色，一个角色拥有多个用户。
2.实体类（省略set，get方法）

public class User {
private int id;
private String name;
private Set roles;
}

 

public class Role {
private int id;
private String name;
private Set users;
}

 
3.数据模型
mysql> desc t_user;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
mysql> desc t_role;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
+-------+--------------+------+-----+---------+----------------+
4.映射文件
User.hbm.xml

<hibernate-mapping>
<class name="com.bjsxt.hibernate.User" table="t_user">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="roles" table="t_user_role">
<key column="userid"/>
<many-to-many class="com.bjsxt.hibernate.Role" column="roleid"/>
</set>
</class>
</hibernate-mapping>

 

Role.hbm.xml

<hibernate-mapping>
<class name="com.bjsxt.hibernate.Role" table="t_role">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<set name="users" table="t_user_role">
<key column="roleid"/>
<many-to-many class="com.bjsxt.hibernate.User" column="userid"/>
</set>
</class>
</hibernate-mapping>

 

<key>中的column属性值必须等于单向关联中<many-to-many>标签指向的column的属性值
<many-to-many>中column属性值必须等于单向关联中<key>中column的属性值
5.测试

public class ManyToManyTest extends TestCase {
//存储
public void testSave(){
Session session = HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
User user1 = new User();
user1.setName("yang9");
session.save(user1);
User user2 = new User();
user2.setName("long1");
session.save(user2);
Set<User> users = new HashSet<User>();
users.add(user1);
users.add(user2);
Role role1 = new Role();
role1.setName("凤山人在线");
role1.setUsers(users);
session.save(role1);
tx.commit();
}
//导入
public void testLoad(){
Session session =HibernateUtils.getSession();
Transaction tx = session.beginTransaction();
Role role = (Role) session.load(Role.class, 1);
System.out.println(role.getName());
for(Iterator ite=role.getUsers().iterator();ite.hasNext();){
User user = (User) ite.next();
System.out.println(user.getName());
}
}