Why hibernate PolymorphismType.EXPLICIT annotation returns the children of a parent on a JPA findAll() search?

Question

Let's say we have a parent class A and a child class B with the inheritance type TABLE_PER_CLASS.

@Entity(name = "A")
@Table(name = "A")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class A{
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    ...........
}


@Entity(name = "B")
@Table(name = "B")
@Polymorphism(type = PolymorphismType.EXPLICIT)
public class B extends A{
    ......
}

And the repository

@Repository
public interface ARepository extends JpaRepository<A, Integer> {
}

Why is when trying to findAll() objects from A we get the objects from B too?

 @RequestMapping(value = "/getAllA", method = RequestMethod.GET)
 public List<A> findAllA() {
    return aRepository.findAll();
}

Shouldn't the @Polymorphism(type = PolymorphismType.EXPLICIT) force the search to return only A objects?

Answer 1

It's because B is also an A. You can use jpql as a workaround to specify the concrete result type you want to fetch:

@Repository
public interface ARepository extends JpaRepository<A, Integer> {

    @Query("select a from A a where type(a) = A")
    List<A> findAll();

}

According to answers to this question this will not work without @DiscriminatorColumn and @DiscriminatorValue annotations.