JPQL语句返回布尔值 [英] JPQL statement returning boolean value

问题描述

是否可以像下面这样编写JPQL查询:

Is it possible to write JPQL query like following:

select count(*) > 0 from Scenario scen where scen.name = :name

根据实体填充条件是否存在将返回true/false布尔值?

that would return true/false boolean values depending of whether entity filling criteria exists or not?

我想以这种方式使用查询:

I would like to use the query this way:

boolean exists = entityManager.createQuery(query,Boolean.class).setParameter("name",name).getSingleResult();

我的示例中的查询在语法上不正确(解析错误)，但是有没有像JPQL中那样进行检查的正确方法，该方法会返回布尔值，还是只能在Java代码中使用? >

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?

推荐答案

是的，可以执行以下操作:

Yes, it is possible with following:

select case when (count(scen) > 0)  then true else false end  
from Scenario scen where scen.name = :name

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