hibernate 多对多剔除解决方案(第二种访求 )

hibernate多对多当中，我们常常希望只删除一方已及对应的关系，但不想删除另一方，怎么样达到呢？?（这里只提删除）

表user和表role多对多，中间表user_role(userId,roleId),user是主控方，role是从方，

在spring+hibernate的环境下，使用的是Annotation配置

?

User.java

@ManyToMany(cascade = {CascadeType.MERGE,CascadeType.PERSIST}, fetch = FetchType.EAGER)
@JoinTable(name = "user_role",

joinColumns = { @JoinColumn(name = "userId",referencedColumnName="userId") },

inverseJoinColumns = { @JoinColumn(name = "roleId",referencedColumnName="roleId") })
?public Set<Role> getRoles() {
??return this.roles;
?}

?

Role.java

@ManyToMany(cascade = {CascadeType.MERGE,CascadeType.PERSIST}, fetch = FetchType.EAGER,

?mappedBy = "roles")
?public Set<User> getUsers() {
??return this.users;
?}

?

测试：主控方User删除，user会被删除，user_role的中的关系也会被删除了，但对应的role不会被删除

@Test
?public void testDelete() {
??User user = userDao.findById(8);
??userDao.delete(user);
?}

测试：从方Role删除，如果user_role里面没有对应的roleId，role可以删除，user不会被删除

@Test
?public void testDelete() {
??Role role = roleDao.findById(26);
??roleDao.delete(role);?

}

测试：从方Role删除，如果user_role里面有对应的roleId和别的userId关联，role不能被删除

@Test
?public void testDelete() {
??Role role = roleDao.findById(26);
??roleDao.delete(role);?

}

会报错：org.springframework.dao.DataIntegrityViolationException: Could not execute JDBC batch update; nested exception is org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

Caused by: org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`hrms`.`user_role`, CONSTRAINT `roleId` FOREIGN KEY (`roleId`) REFERENCES `role` (`roleId`) ON DELETE NO ACTION ON UPDATE NO ACTION)

解决方案：在数据库里更改user_role表结构，就是添加约束，就添加roleId的删除时进行级联操作

ALTER TABLE `hrms`.`user_role`

? ADD CONSTRAINT `roleId`

? FOREIGN KEY (`roleId` )

? REFERENCES `hrms`.`role` (`roleId` )

??ON DELETE CASCADE;

?

测试：从方Role删除,如果user_role里面有对应的roleId,现在role可以删除,user_role里面对应的关系也会被删除，但对应的user不会被删除，达到我们想要的效果

@Test
?public void testDelete() {
??Role role = roleDao.findById(26);
??roleDao.delete(role);?

}