使用单表策略持久化 Hibernate 继承映射

Question

I'm using the single table strategy to persist data, my (example) structure looks like this:

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Musician {

    @Id
    private Integer id;

    private String name;

    // getters, setters
}

With sub-classes as such:

@Entity
public class MusicianGuitar extends Musician {
}

@Entity
public class MusicianVocals extends Musician {
}

Each sub-class also has it's own repository class which simply looks like this:

public interface MusicianGuitarRepository extends JpaRepository<MusicianGuitar, Integer> {
}

public interface MusicianVocalRepository extends JpaRepository<MusicianVocal, Integer> {
}

I'm reading a collection of them from a source, but I want to write the saving method to be re-usable.. this is what I currently have:

private void saveGuitarists(List<MusicianGuitar> guitarists) {
    for (MusicianGuitar guitarist : guitarists) {
        MusicianGuitar existingGuitarist = guitaristRepository.findByName(guitarist.getName());
        if (existingGuitarist == null) {
            MusicianGuitar newGuitarist = new MusicianGuitar();
            newGuitarist.setName("Slash");
            guitaristRepository.save(newGuitarist);
        }
    }
}

.. and similarly for saveVocalists, saveDrummers, etc

The problem is I have to write this kind of method out for every type of Musician I currently have, and will have to write it again if there's new types added later - in this example and my practical one, the objects have all the same fields, they are just of differing types. I considered passing a Musician enum type, but that doesn't make things anything simpler. I suspect there's some way I can leverage the inheritance mapping, but can't see how.. thanks in advance!

Answer 1

You can try to use something like that

private void saveGuitarists(List<? extends Musician> musicians) {
   for (Musician musician : musicians) {
        Musician existingMusician = musicianRepository.findByName(musician.getName());
        if (existingMusician == null) {
            // create Musician and populate fields
            musicianRepository.save(newMusician);
        }
    }
}