通过联接表进行JPA查询 [英] JPA Query over a join table

问题描述

我有3张桌子，例如:

A                              AB                        B
-------------                  ------------              ---------------
a1                              a1,b1                    b1

AB是A和B之间的转换表

AB is a transition table between A and B

有了这个，我的班级在这两个班级之间没有组成.但是我想知道，使用JPQL查询，是否存在AB表中A表中我的元素的任何记录.我只需要数字或布尔值即可.

With this, my classes have no composition within these two classes to each other. But I want to know that , with a JPQL Query, if any records exist for my element from A table in AB table. Just number or a boolean value is what I need.

由于AB是一个过渡表，因此没有模型对象，我想知道是否可以通过Repository对象中的@Query来做到这一点.

Because AB is a transition table, there is no model object for it and I want to know if I can do this with a @Query in my Repository object.

推荐答案

我建议使用本地查询方法界面(JPA也支持本地查询).让我们假设表A是客户，表B是产品，而AB是销售.这是获取客户订购产品列表的查询.

I suggest to use Native query method intead of JPQL (JPA supports Native query too). Let us assume table A is Customer and table B is a Product and AB is a Sale. Here is the query for getting list of products which are ordered by a customer.

entityManager.createNativeQuery("SELECT PRODUCT_ID FROM 
                                     SALE WHERE CUSTOMER_ID = 'C_123'");

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