问题
Is it possible to write JPQL query like following:
select count(*) > 0 from Scenario scen where scen.name = :name
that would return true/false boolean values depending of whether entity filling criteria exists or not?
I would like to use the query this way:
boolean exists = entityManager.createQuery(query,Boolean.class).setParameter("name",name).getSingleResult();
The query from my example just isn't syntactically correct (parse error), but is there any correct way of doing checks like that in JPQL, that would return boolean value, or is it only possible in Java code?
回答1:
Yes, it is possible with following:
select case when (count(scen) > 0) then true else false end
from Scenario scen where scen.name = :name
回答2:
What about just:
select count(scen) > 0
from Scenario scen where scen.name = :name
回答3:
I was having the same problem, then I updated my hibernate to 4.3.11.Final and now it's working.
来源：https://stackoverflow.com/questions/12051563/jpql-statement-returning-boolean-value