Hibernate manytomany实现

在hibernate中，多对多关系可以看成是2个多对一的关系。

在实体UserInfo和Teacher中，都设置many-to-many属性,

　　属性中需要设置主控方与被控方的inverse和cascade值

出现问题：save the transient instance before flushing

说明：t_s表，不需要单独建实体对象，是一张表

 1 CREATE TABLE t_s
 2 (
 3   u_id integer NOT NULL,
 4   t_id integer NOT NULL,
 5   CONSTRAINT t_s_pkey PRIMARY KEY (u_id, t_id),
 6   CONSTRAINT t_s_t_id_fkey FOREIGN KEY (t_id)
 7       REFERENCES teacher (id) MATCH SIMPLE
 8       ON UPDATE NO ACTION ON DELETE NO ACTION,
 9   CONSTRAINT t_s_u_id_fkey FOREIGN KEY (u_id)
10       REFERENCES userinfo (id) MATCH SIMPLE
11       ON UPDATE NO ACTION ON DELETE NO ACTION
12 )

UserInfo.hbm.cfg

1 <set name="teachers" table="t_s" inverse="false" cascade="all">
2             <key column ="u_id"></key>
3             <many-to-many class="Teacher" column="t_id"></many-to-many>
4         </set>

　　Teacher.hbm.cfg

1 <set name="students" table="t_s" inverse="true" cascade="all">
2             <key column ="t_id"></key>
3             <many-to-many class="UserInfo" column="u_id"></many-to-many>
4         </set>

测试代码：（*主控方与被控方的设置，先设主控方，在设被控方）

 1     ///多对多操作
 2     private static void ManyToMany()
 3     {
 4         Session session=HibernateUnit.getSession();
 5         session.beginTransaction();
 6         
 7         UserInfo u1=new UserInfo();
 8         UserInfo u2=new UserInfo();
 9         
10         Teacher t1=new Teacher();
11         Teacher t2=new Teacher();
12         
13         u1.setUsername("CC");
14         u1.setAge(20);
15         u1.setAddress("1111");
16         u1.setCg(null);
17         
18         u2.setUsername("MR");
19         u2.setAge(20);
20         u2.setAddress("1111");
21         u2.setCg(null);
22         
23         t1.setName("JiangRR");
24         t2.setName("ChenXD");
25 
26         u1.getTeachers().add(t1);
27         u2.getTeachers().add(t2);
28         t1.getStudents().add(u1);
29         t2.getStudents().add(u2);
30 
31         session.save(u1);
32         session.save(u2);
33         
34         session.getTransaction().commit();
35     }

测试效果：

 1 Hibernate: select nextval ('userinfo_id_seq')
 2 Hibernate: select nextval ('teacher_id_seq')
 3 Hibernate: select nextval ('userinfo_id_seq')
 4 Hibernate: select nextval ('teacher_id_seq')
 5 Hibernate: insert into userinfo (username, age, address, id) values (?, ?, ?, ?)
 6 Hibernate: insert into teacher (username, id) values (?, ?)
 7 Hibernate: insert into userinfo (username, age, address, id) values (?, ?, ?, ?)
 8 Hibernate: insert into teacher (username, id) values (?, ?)
 9 Hibernate: insert into t_s (u_id, t_id) values (?, ?)
10 Hibernate: insert into t_s (u_id, t_id) values (?, ?)