标签：strong 可见 拒绝 运行 nts 完整 log into set
mappedBy:
所填内容必为本类在另一方的字段名。
表示：本类放弃控制关联关系，所有对关联关系的控制，如：建立、解除与另一方的关系，都由对方控制，本类不管。举个例子：
Teacher和Student之间是多对多关联关系，在Student端的teachers字段的@ManyToMany注解里面，配置属性mappedBy = "students"。表示：学生没有资格控制与老师的关联关系(如：建立关系、删除关系)，只有老师才有资格控制关联关系。学生不能说：”我们两做朋友吧“。(即使说了，也无济于事，老师当学生没说。即Hibernate把学生说的当作耳边风，虽然Hibernate也不会抛出异常，程序照样能运行)。但是，老师可以说，“我们做朋友吧”。那么，学生只能无任何拒绝理由地接受。同样，如果学生说，”我们从此一刀两断吧“，那也是没用的。只有老师说：“滚，有多远，滚多远，为师今日将你逐出师门，再也不想见到你”，那么，这才能有效地解除关联关系(注意：这是一个对象(对应数据库里的一行记录)和一个对象之间的关系，而不是表和表之间的关联关系。一对师生关系的解除，不能影响整个社会的师生关系)。
测试代码：(这是完整类，后面只贴出test1的代码，其他部分不变)
public class MappedByTest { private static SessionFactory sessionFactory; private Session session; @BeforeClass public static void beforeTest(){ sessionFactory = HibernateUtil.getSessionFactory(); } @AfterClass public static void afterTest(){ sessionFactory.close(); } @Before public void beginTransaction(){ session = sessionFactory.openSession(); session.beginTransaction(); } @After public void commitTransaction(){ session.getTransaction().commit(); session.close(); } @Test public void execute(){ test1(); } public void test1(){ Student student1 = new Student("学生张三",3); Student student2 = new Student("学生李四",4); Teacher teacher1 = new Teacher("老师王五",5); Teacher teacher2 = new Teacher("老师赵六",6); List<Student> students = new ArrayList<>(); students.add(student1); students.add(student2); List<Teacher> teachers = new ArrayList<>(); teachers.add(teacher1); teachers.add(teacher2); session.save(teacher1); session.save(teacher2); student1.setTeachers(teachers); session.save(student1); } }
产生的结果：
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然后，清空数据库，做第二次测试：
public void test1() { Student student1 = new Student("学生张三", 3); Student student2 = new Student("学生李四", 4); Teacher teacher1 = new Teacher("老师王五", 5); Teacher teacher2 = new Teacher("老师赵六", 6); List<Student> students = new ArrayList<>(); students.add(student1); students.add(student2); List<Teacher> teachers = new ArrayList<>(); teachers.add(teacher1); teachers.add(teacher2); session.save(student1); session.save(student2); teacher1.setStudents(students); session.save(teacher1); }
产生的结果：
可见：在Student类的teachers字段的@ManyToMany注解上配置属性mappedBy = "students"，所有Student类产生的对象均不能建立和老师的关联关系，只有老师可以。
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然后，清空数据库，做第三次测试：
public void test1(){ Student student1 = new Student("学生张三",3); Student student2 = new Student("学生李四",4); Teacher teacher1 = new Teacher("老师王五",5); Teacher teacher2 = new Teacher("老师赵六",6); List<Student> students = new ArrayList<>(); students.add(student1); students.add(student2); List<Teacher> teachers = new ArrayList<>(); teachers.add(teacher1); teachers.add(teacher2); int stuId = 4; int teacherId = 6; Student persistentStudent = (Student)session.get(Student.class, stuId); Teacher persistentTeacher = (Teacher)session.get(Teacher.class, teacherId); persistentStudent.getTeachers().remove(persistentTeacher); session.update(persistentStudent); }
控制台打出的SQL语句：
Hibernate: select student0_.student_id as student_1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from student student0_ where student0_.student_id=? Hibernate: select teacher0_.teacher_id as teacher_1_1_0_, teacher0_.age as age2_1_0_, teacher0_.name as name3_1_0_ from teacher teacher0_ where teacher0_.teacher_id=? Hibernate: select teachers0_.student_id as student_2_2_0_, teachers0_.teacher_id as teacher_1_2_0_, teacher1_.teacher_id as teacher_1_1_1_, teacher1_.age as age2_1_1_, teacher1_.name as name3_1_1_ from ts_relation teachers0_ inner join teacher teacher1_ on teachers0_.teacher_id=teacher1_.teacher_id where teachers0_.student_id=?
产生的结果：
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然后，清空数据库，做第四次测试：
public void test1(){ Student student1 = new Student("学生张三",3); Student student2 = new Student("学生李四",4); Teacher teacher1 = new Teacher("老师王五",5); Teacher teacher2 = new Teacher("老师赵六",6); List<Student> students = new ArrayList<>(); students.add(student1); students.add(student2); List<Teacher> teachers = new ArrayList<>(); teachers.add(teacher1); teachers.add(teacher2); int stuId = 4; int teacherId = 6; Student persistentStudent = (Student)session.get(Student.class, stuId); Teacher persistentTeacher = (Teacher)session.get(Teacher.class, teacherId); persistentTeacher.getStudents().remove(persistentStudent); session.update(persistentTeacher); }
控制台打出的SQL语句：
Hibernate: select student0_.student_id as student_1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from student student0_ where student0_.student_id=? Hibernate: select teacher0_.teacher_id as teacher_1_1_0_, teacher0_.age as age2_1_0_, teacher0_.name as name3_1_0_ from teacher teacher0_ where teacher0_.teacher_id=? Hibernate: select students0_.teacher_id as teacher_1_2_0_, students0_.student_id as student_2_2_0_, student1_.student_id as student_1_0_1_, student1_.age as age2_0_1_, student1_.name as name3_0_1_ from ts_relation students0_ inner join student student1_ on students0_.student_id=student1_.student_id where students0_.teacher_id=? Hibernate: --------------------------注意这条 delete from ts_relation where teacher_id=? Hibernate: insert into ts_relation (teacher_id, student_id) values (?, ?)
产生的结果：
可见：在Student类的teachers字段的@ManyToMany注解上配置属性mappedBy = "students"，所有Student类产生的对象均不能删除和老师的关联关系，只有老师可以。
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由此证明了之前所说的，mappedBy表示，本类防止控制和另一方的关联关系，所填内容必为本类在另一方的字段名。
标签：strong 可见 拒绝 运行 nts 完整 log into set
原文地址：http://www.cnblogs.com/565261641-fzh/p/6653847.html
