Spring Data JPA 和 Exists 查询 [英] Spring Data JPA and Exists query
问题描述
我正在使用 Spring Data JPA(使用 Hibernate 作为我的 JPA 提供程序)并且想要定义一个带有 HQL 查询的 exists
方法:
I'm using Spring Data JPA (with Hibernate as my JPA provider) and want to define an exists
method with a HQL query attached:
public interface MyEntityRepository extends CrudRepository<MyEntity, String> {
@Query("select count(e) from MyEntity e where ...")
public boolean existsIfBlaBla(@Param("id") String id);
}
当我运行这个查询时,我得到一个 java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Boolean
.
When I run this query, I get a java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Boolean
.
HQL 查询必须是什么样子才能完成这项工作?我知道我可以简单地返回一个 Long 值,然后如果 count >0
,但是这种解决方法应该不是必需的,对吧?
How does the HQL query have to look like to make this work? I know I could simply return a Long value and afterwards check in my Java code if count > 0
, but that workaround shouldn't be necessary, right?
推荐答案
我认为您可以简单地更改查询以返回布尔值
I think you can simply change the query to return boolean as
@Query("select count(e)>0 from MyEntity e where ...")
附注:如果您根据主键值检查是否存在 CrudRepository
已经有 exists(id)
方法.
PS:
If you are checking exists based on Primary key value CrudRepository
already have exists(id)
method.
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