Hibernate学习15 -- 关联映射5 -- 多对多关联1 -- 多对多关联单向

一般的设计中，多对多关联映射，需要一个中间表,Hibernate会自动生成中间表,Hibernate使用many-to-many标签来表示多对多的关联。多对多的关联映射，在实体类中，跟一对多一样，也是用集合来表示的。

步骤：

n         建立POJO:User.java，Role.java，建立hibernate的配置文件，将两个hbm文件与其绑定

n         在User.java里面建立一个Set类型的属性，准备Role对象

n         代码实现：

User.java

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

Role.java

public class Role {     private int id;     private String name;

User.hbm.xml

<hibernate-mapping>     <class name="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="Role" column="roleid"/>        </set>     </class> </hibernate-mapping>

Role.hbm.xml

<hibernate-mapping>     <class name="Role" table="t_role">        <id name="id">            <generator class="native"/>        </id>        <property name="name"/>     </class> </hibernate-mapping>

测试类：

public class Many2Many extends TestCase {     public void testSave() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();                   Role r1 = new Role();            r1.setName("数据录入人员");            session.save(r1);                   Role r2 = new Role();            r2.setName("商务主管");            session.save(r2);                   Role r3 = new Role();            r3.setName("大区经理");            session.save(r3);                   User u1 = new User();            u1.setName("张三");            Set u1Roles = new HashSet();            u1Roles.add(r1);            u1Roles.add(r2);            u1.setRoles(u1Roles);                      User u2 = new User();            u2.setName("李四");            Set u2Roles = new HashSet();            u2Roles.add(r2);            u2Roles.add(r3);            u2.setRoles(u2Roles);                      User u3 = new User();            u3.setName("王五");            Set u3Roles = new HashSet();            u3Roles.add(r1);            u3Roles.add(r2);            u3Roles.add(r3);            u3.setRoles(u3Roles);                      session.save(u1);            session.save(u2);            session.save(u3);                   session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }              public void testLoad() {        Session session = null;        try {            session = HibernateUtils.getSession();            session.beginTransaction();            User user = (User)session.load(User.class, 1);            System.out.println(user.getName());            for (Iterator iter=user.getRoles().iterator();  iter.hasNext();) {               Role role = (Role)iter.next();               System.out.println(role.getName());            }            session.getTransaction().commit();        }catch(Exception e) {            e.printStackTrace();            session.getTransaction().rollback();        }finally {            HibernateUtils.closeSession(session);        }     }          }