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：
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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：
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<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
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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：
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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：
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<!— 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。