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 (?, ?)