Alternatives to getReference method in Spring data JPA

Question

I found myself struggling to implement customizable methods in Spring Data JPA. For example, I have a Pet class, which has an Owner(Many to One rel.) What if I have a method to save(Pet pet, int ownerId). How can I get ownerId? Using Hibernate I just can getReference like that

public Pet save(Pet pet, int ownerId) {
        if (!pet.isNew() && get(pet.getId(), ownerId) == null) {
            return null;
        }
        pet.setUser(em.getReference(Owner.class, ownerId));
        if (pet.isNew()) {
            em.persist(pet);
            return pet;
        } else {
            return em.merge(pet);
        }
    }

But using a Spring DJPA it's not so easy. I've created an interface that extends JpaRepository < Pet, Integer >, hoping that the parent class has a method called saveWithReference, but i didn't find anything.. Any ideas guys?

Answer 1

You should have both a PetRepository and OwnerRepository both extending JpaRepository.

public interface PetRepository extends JpaRepository<Pet, Long> {}

and

public interface OwnerRepository extends JpaRepository<Owner, Long> {}

Using Spring Data JPA you can use the getOne method to get a reference, this in contrast to the findOne which will actually query the database.

The code you wrote using the EntityManager is basically the same and you should put that in a service method and instead of directly using the EntityManager use the 2 repositories.

@Service
@Transactional
public PetService {

    private final PetRepository pets;
    private final OwnerRepository owners;

    public PetService(PetRepository pets, OwnerRepository owners) {
        this.pets=pets;
        this.owners=owners;
    }

    public Pet savePet(Pet pet, long ownerId) {
        if (!pet.isNew() && get(pet.getId(), ownerId) == null) {
            return null;
        }
        pet.setUser(owners.getOne(ownerId));
        return pets.save(pet);
    }
}

Something like that should do the trick. NO need to implement methods in your repository.