Question

我想在JPA中加入3个表的联接。这是3张桌子：

USER [（pk）userId，登录名和密码];
任务[（pk）taskId，任务名，开始，结束，＃userId]；
TASK_USER [（cmp）taskId，（cmp）userId];

这是要在JPA中执行的SQL查询：

SELECT tu.taskId, t.start, t.end 
  FROM task as t, 
       user as u, 
       task_user as tu 
 WHERE (tu.taskId = t.taskId 
   AND tu.userId = u.userId 
   AND t.userId = u.userId) 
   AND tu.userId = '2';

但是给我带来问题的是应JPA请求编写的语法。

你能帮我吗？

Answer 1

尝试一下：

SELECT tu.taskId, t.start, t.end FROM task as t inner join user as u
on u.userId = t.userId inner join task_user as tu on tu.taskId = t.taskId
where tu.userId = '2';

Answer 2

SELECT tu.taskId, t.start, t.end 
FROM task as t, user as u, task_user as tu 
WHERE tu.taskId = t.taskId AND tu.userId = u.userId 
      AND t.userId = u.userId 
      AND tu.userId = '2';

Answer 3

如果您已使用ManyToMany关系定义了实体之间的关系如果不是https://vladmihalcea.com/the-best-way-to-use-the-manytomany-annotation-with-jpa-and-hibernate/

，请检查此内容

您可以编写这种查询

SELECT t.taskId, t.start, t.end FROM User as u left join u.tasks WHERE u.userId = '2';

Answer 4

谢谢，没关系。我可以在JPA中将查询编写为SQL。语法与SQL相同，我可以返回一个对象作为示例：join中的用户对象

如何在JPA中联接3个表？

4 个答案: