How to reference the 'normal' spring data repo from a custom implementation?

Question

I want to extend a JpaRepository with a custom implementation, so i add a MyRepositoryCustom interface and a MyRepositoryImpl class ex

Answer 1

The section titled Adding custom behaviour to all repositories in the documentation should help you.

For example (only for illustration purposes):

public interface ExtendedJpaRepository<T, ID extends Serializable>
       extends JpaRepository<T, ID> {
    T findFirst();
    T findLast();
}

public class ExtendedJpaRepositoryImpl<T, ID extends Serializable>
       extends SimpleJpaRepository<T, ID>
       implements ExtendedJpaRepository<T, ID> {
  public ExtendedJpaRepositoryImpl(Class<T> domainClass, EntityManager em) {
    super(domainClass, entityManager);
  }

  public T findFirst() {
    List<T> all = findAll();

    return !all.isEmpty() ? all.get(0) : null;
  }

  public T findLast() {
    List<T> all = findAll();

    return !all.isEmpty() ? all.get(all.size() - 1) : null;
  }
}

Then, configure ExtendedJpaRepositoryImpl for use as per the instructions given in the documentation linked above.

Since ExtendedJpaRepositoryImpl extends SimpleJpaRepository (which is an implementation of JpaRepository), all methods from JpaRepository can be called from ExtendedJpaRepositoryImpl.

Answer 2

tl;dr

To inject the core repository interface into a custom implementation, inject a Provider<RepositoryInterface> into the custom implementation.

Details

The core challenge to get that working is setting up the dependency injection correctly as you are about to create a cyclic dependency between the object you're about to extend and the extension. However this can be solved as follows:

interface MyRepository extends Repository<DomainType, Long>, MyRepositoryCustom {
  // Query methods go here
}

interface MyRepositoryCustom {
  // Custom implementation method declarations go here
}

class MyRepositoryImpl implements MyRepositoryCustom {

  private final Provider<MyRepository> repository;

  @Autowired
  public MyRepositoryImpl(Provider<MyRepository> repository) {
    this.repository = repository;
  }

  // Implement custom methods here
}

The most important part here is using Provider<MyRepository> which will cause Spring to create a lazily-initialized proxy for that dependency even while it's creating an instance for MyRepository in the first place. Inside the implementation of your custom methods you can then access the actual bean using the ….get()-method.

Provider is an interface from the @Inject JSR and thus a standardized interface and requires an additional dependency to that API JAR. If you want to stick to Spring only, you can used ObjectFactory as an alternative interface but get the very same behavior.