HQL留下了不相关实体的连接 [英] HQL left join of un-related entities

问题描述

我有两个实体， A 和 B 。它们是相关的，但我不想将关系映射添加到bean。

I have 2 entities, A and B. They are related but I do not want to add the relationship mapping to the beans.

我们如何在 A之间使用左外连接和 B 使用HQL或标准？

How can we use left outer join between A and B using HQL or criteria?

有一些解决方法可用于此，

There are some workarounds available for this,

1. 按照


2. 添加关系并使用从A中选择一个左连接ab
。

3. 我们可以在HQL中执行内部连接，如 select * from a a，B b其中a.some = b.some

1. Use Native SQL as told here.
2. Add a relationship and use select a from A a left join a.b.
3. We can do a inner join in the HQL as select * from A a, B b where a.some=b.some

我总是回顾这两个选项，对此有没有其他选择？或者这样做是不可能的？

I was always going back these 2 options, is there any alternative for this? Or this in not possible?

推荐答案

目前，使用HQL的where子句中加入不相关类的t​​heta样式仅支持内部连接。

Currently, the theta-style on joining the unrelated classes in the where clause using HQL only supports inner join.

请求为了支持这种情况的外连接，目前是第3次投票最多的增强，但我不认为这个功能将在近端功能中实现，因为它需要重新实现当前基于ANTLER的查询解析器，这似乎是一项巨大的IMO任务。

The request for supporting the outer join for such situation is currently the 3-rd most voted enhancement but I don't think this feature will be implemented in the near feature as it requires the re-implementation of the current ANTLER-based query parser first which seems to be a gigantic task IMO.

如果您坚持使用HQL执行左连接而不添加A和B之间的关系，则可以使用选项3首先执行内连接，然后使用follow ng HQL

If you insist to use the HQL to perform left join without adding the relationship between A and B , you can use option 3 to do the inner join first, then use the following HQL

from A a where a.some not in ( select b.some from B)

查找所有无法加入B并以编程方式结合结果的A。

to find out all the A that cannot join B and combine the results programmatically .

自版本5.1.0开始 HHH-16（Explicit joins on unrelated classes） is fixed，we should be能够加入不相关的实体。

As of release 5.1.0 HHH-16 (Explicit joins on unrelated classes) is fixed and we should be able to join the unrelated entities.

这篇关于HQL留下了不相关实体的连接的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！