如何防止Hibernate中出现空列表错误？

Question

我在hibernate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)

除非子查询（select o.item from Opinion as o where o.user =:user）返回空列表，否则此查询正常工作。在这种情况下，我收到了一个错误。

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

如何重写查询以使其在空（select o.item from Opinion as o where o.user =:user）下工作？

Answer 1

我看到的一个微不足道的方式是

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)