Spring Data Jpa中的子查询 [英] Sub-Query in Spring Data Jpa

问题描述

我在jpql中有这样的查询

I have query like this in jpql

select new com.example.CustomGroup(m.id, m.title, (select count(w.id) from MessageGroup x join x.messages w where w.readers.id <> ?1) ) 
from MessageGroup m join m.members u where u.id = ?1

但无法正常工作，我知道jpa 2支持select中的子查询，但找不到任何关于如何使用它的提示

but not work, i know jpa 2 support sub query in select but cant find any refrence to how use it

推荐答案

摘自JPA 2.2规范，第4.6.16段:

Quote from the JPA 2.2 specification, paragraph 4.6.16:

子查询可以在WHERE或HAVING子句中使用.[66]

Subqueries may be used in the WHERE or HAVING clause.[66]

[66]在此版本中，子查询仅限于WHERE和HAVING子句.在本规范的更高版本中，将考虑对FROM子句中的子查询的支持.

[66] Subqueries are restricted to the WHERE and HAVING clauses in this release. Support for subqueries in the FROM clause will be considered in a later release of this specification.

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