spring - 如何防止休眠中的空列表错误？

Question

我在休眠中有以下 HQL 查询：

select x 
from Item as x
where x not in (select o.item from Opinion as o where o.user =:user)

此查询工作正常，除非子查询 ( select o.item from Opinion as o where o.user =:user) 返回一个空列表。在这种情况下，我得到了一个错误。

select o.item from Opinion as o where o.user =:user当子查询（）为空时，有没有办法防止 Hibernate 引发错误？

我如何必须重写查询以使其即使对于空 ( select o.item from Opinion as o where o.user =:user) 也能正常工作？

score 0 · Accepted Answer

我看到的一种简单方法是

select x 
from Item as x
where (select count(distinct o.item) from Opinion as o where o.user =:user) = 0

或（*未经测试）

select x 
from Item as x
where not exists (from Opinion as o where o.item = x and o.user =:user)

1 回答 1