多对多的关系操作
2015-09-04 15:05
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把表建好了之后,我们来进行多对多的关系操作。
运行之后,三张表都增加了数据:
course:
student:
student_course:
E:把一个课程,更改为另外一个课程:
由于我自己添加了一些课程,在这里没有把代码展示出来
结果如图
把一个学生加入到一些课程中:
操作结果为:
Hibernate: select student0_.sid as sid2_0_, student0_.sdescription as sdescrip2_2_0_, student0_.sname as sname2_0_ from Student student0_ where student0_.sid=?
Hibernate: select course0_.cid as cid0_, course0_.cname as cname0_, course0_.cdescription as cdescrip3_0_ from Course course0_ where course0_.cid in (1 , 2 , 3)
Hibernate: select courses0_.sid as sid2_1_, courses0_.cid as cid1_, course1_.cid as cid0_0_, course1_.cname as cname0_0_, course1_.cdescription as cdescrip3_0_0_ from student_course courses0_ inner join Course course1_ on courses0_.cid=course1_.cid where courses0_.sid=?
Hibernate: insert into student_course (sid, cid) values (?, ?)
Hibernate: insert into student_course (sid, cid) values (?, ?)
Hibernate: insert into student_course (sid, cid) values (?, ?)
public void saveStudent_cascade_Course(){ Session session=sessionFactory.openSession(); Transaction transaction=session.beginTransaction(); Student student=new Student(); student.setSname("ansel"); student.setSdescription("nice"); Course course=new Course(); course.setCdescription("exciting"); course.setCname("PE"); Set<Course> courses=new HashSet<Course>(); courses.add(course); student.setCourses(courses); /** * 注意:这里是保存的student,因为我们在上面设置的是student的属性, 要找准,如果在这里找错了,就直接保存到save里面的对象,剩下的表会没有内容的 */ session.save(student); transaction.commit(); session.close(); }
运行之后,三张表都增加了数据:
course:
student:
student_course:
E:把一个课程,更改为另外一个课程:
public void transferCourse(){ Session session=sessionFactory.openSession(); Transaction transaction=session.beginTransaction(); //获取到学生 Student student=(Student)session.get(Student.class, 1L); //获取到要更改的课程 Course course=(Course)session.get(Course.class, 1L); //把要更改的课程移除 student.getCourses().remove(course); //获取目标课程 Course course2=(Course)session.get(Course.class, 2L); //添加目标课程 student.getCourses().add(course2); transaction.commit(); session.close(); }
由于我自己添加了一些课程,在这里没有把代码展示出来
结果如图
把一个学生加入到一些课程中:
public void testSaveStudent_cascade_Course(){ //把一个学生添加到id1、2、3的课程中 Session session=sessionFactory.openSession(); Transaction transaction=session.beginTransaction(); //得到学生 Student student=(Student) session.get(Student.class, 3L); //得到123课程的集合,这里使用的是hql语句,注意是从pojo类中找 List<Course> courses=session.createQuery("from Course where cid in (1,2,3)").list(); //设置学生的课程,这个学生可能原来有课程 student.getCourses().addAll(courses); transaction.commit(); session.close(); }
操作结果为:
Hibernate: select student0_.sid as sid2_0_, student0_.sdescription as sdescrip2_2_0_, student0_.sname as sname2_0_ from Student student0_ where student0_.sid=?
Hibernate: select course0_.cid as cid0_, course0_.cname as cname0_, course0_.cdescription as cdescrip3_0_ from Course course0_ where course0_.cid in (1 , 2 , 3)
Hibernate: select courses0_.sid as sid2_1_, courses0_.cid as cid1_, course1_.cid as cid0_0_, course1_.cname as cname0_0_, course1_.cdescription as cdescrip3_0_0_ from student_course courses0_ inner join Course course1_ on courses0_.cid=course1_.cid where courses0_.sid=?
Hibernate: insert into student_course (sid, cid) values (?, ?)
Hibernate: insert into student_course (sid, cid) values (?, ?)
Hibernate: insert into student_course (sid, cid) values (?, ?)
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