Spring Data JPA. How to get only a list of IDs from findAll() method

Question

I have a very complicated model. Entity has a lot relationship and so on.

I try to use Spring Data JPA and I prepared a repository.

but when I invoke a met

Answer 1

Why not using the @Query annotation?

@Query("select p.id from #{#entityName} p")
List getAllIds();

The only disadvantage I see is when the attribute id changes, but since this is a very common name and unlikely to change (id = primary key), this should be ok.