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 method findAll() with specification for the object a have a performance issue because objects are very big. I know that because when I invoke a method like this:

@Query(value = "select id, name from Customer ") List<Object[]> myFindCustomerIds(); 

I didn't have any problems with performance.

But when I invoke

List<Customer> findAll();  

I had a big problem with performance.

The problem is that I need to invoke findAll method with Specifications for Customer that is why I cannot use method which returns a list of arrays of objects.

How to write a method to finding all customers with specifications for Customer entity but which returns only an IDs.

like this:

List<Long> findAll(Specification<Customer> spec); 

• I cannot use in this case pagination.

Please help.

Answer 1

Why not using the @Query annotation?

@Query("select p.id from #{#entityName} p") List<Long> 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.