HQL 左连接不相关的实体 [英] HQL left join of un-related entities

问题描述

我有 2 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.

我们如何使用 HQL 或标准在 A 和 B 之间使用左外连接?

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

对此有一些解决方法，

1. 按照此处的说明使用本机 SQL.
2. 添加关系并使用select a from A a left join a.b.
3. 我们可以在 HQL 中进行内连接，如select * from A a, B b where 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

我总是回到这两个选项，有什么替代方法吗?或者这是不可能的?

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 在 where 子句中加入无关类的 theta 样式仅支持内连接.

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

在这种情况下支持外连接的请求是目前投票数第三的增强 但我不认为这个特性会在 Near 特性中实现，因为它需要 re-首先实现当前基于 ANTLER 的查询解析器，这在 IMO 看来是一项巨大的任务.

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.

如果你坚持使用HQL进行左连接而不添加A和B之间的关系，你可以使用选项3先做内连接，然后使用下面的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)

找出所有不能加入B的A并以编程方式组合结果.

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

更新

从 5.1.0 版开始 HHH-16(不相关类的显式连接) 已修复，我们应该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.

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