多对多关联映射 双向 两方都持有对象引用，修改对象模型,但数据的存储没有变化。
再修改映射文件：
public class Role {
private int id;
private String name;
private Set users;//users对象的集合
public int getUsers() {
return users;
}
public void setUsers(int users) {
this.users= users;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Role映射文件：
<hibernate-mapping>
<class name="com.wjt276.hibernate.Role" table="t_role">
<id name="id">
<generator class="native"/>
</id>
<property name="name" column="name"/>
<!— order-by 属性是第三方表哪个字段进行排序-->
<set name="users" table="t_user_role" order-by="userid">
<key column="roleid"/>
<many-to-many class="com.wjt276.hibernate.User" column="userid"/>
</set>
</class>
</hibernate-mapping>
注：数据的存储与单向一样。但一般维护这个多对多关系，只需要使用一方，而使另一方维护关系失效。
多对多关联映射双向数据加载
session = HibernateUtils.getSession();
tx = session.beginTransaction();
Role role = (Role)session.load(Role.class, 1);
System.out.println("role.name=" + role.getName());
for (Iterator<User> iter = role.getUsers().iterator();iter.hasNext();){
User user = iter.next();
System.out.println("user.name=" + user.getName());
}
//提交事务
tx.commit();
生成SQL语句：
|
Hibernate: select role0_.id as id2_0_, role0_.name as name2_0_ from t_role role0_ where role0_.id=? role.name=数据录入人员 Hibernate: select users0_.roleid as roleid1_, users0_.userid as userid1_, user1_.id as id0_0_, user1_.name as name0_0_ from t_user_role users0_ left outer join t_user user1_ on users0_.userid=user1_.id where users0_.roleid=? order by users0_.userid user.name=10 user.name=成龙 |
总结：
<!— order-by 属性是第三方表哪个字段进行排序-->
<set name="users" table="t_user_role" order-by="userid">
<key column="roleid"/>
<many-to-many class="com.wjt276.hibernate.User" column="userid"/>
</set>
- table属性值必须和单向关联中的table属性值一致
- <key>中column属性值要与单向关联中的<many-to-many>标签中的column属性值一致
- 在<many-to-many>中的column属性值要与单向关联中<key>标签的column属性值一致。