Hibernate中ManytoMany中save（）方法的问题

[Luger]

	@Test
	public void testInsertTeacher() {
		Student s = new Student();
		s.setAge(20);
		
		Student s1 = new Student();
		s1.setAge(22);
		
		Teacher t = new Teacher();
		t.setName("Xue");
		
		Teacher t2 = new Teacher();
		t2.setName("Han");
		
		t.getStudents().add(s);
		t.getStudents().add(s1);
		t2.getStudents().add(s);
		
		Session session = sf.getCurrentSession();
		session.beginTransaction();
     	session.save(t);
     	session.save(t2);
		session.getTransaction().commit();
	}
	
	
	@Test
	public void testInsertStudent() {   //Something wrong with this method
		Student s = new Student();
		s.setAge(20);
		
		Student s1 = new Student();
		s1.setAge(22);
		
		Teacher t = new Teacher();
		t.setName("Xue");
		
		Teacher t2 = new Teacher();
		t2.setName("Han");
		
		s.getTeachers().add(t);
		s1.getTeachers().add(t2);
		
		Session session = sf.getCurrentSession();
		session.beginTransaction();
		session.save(s);
		session.getTransaction().commit();
	}

这个代买中insertTeacher就没有问题 在saveTeacher的同时会在中间表中插入对应的外键连接 但是插入Student的时候就不行 Why？

[Luger]

有人解决吗？