How to add custom method to Spring Data JPA

Question

I am looking into Spring Data JPA. Consider the below example where I will get all the crud and finder functionality working by default and if I want to customize a finder t

Answer 1

As specificed in the documented functionality, the Impl suffix allows us to have a clean solution:

• Define in the @Repository interface, say MyEntityRepository, either Spring Data methods or custom methods
• Create a class MyEntityRepositoryImpl (the Impl suffix is the magic) anywhere (doesn't even need to be in the same package) that implements the custom methods only and annotate such class with @Component** (@Repository will not work).
  • This class can even inject MyEntityRepository via @Autowired for use in the custom methods.

Example:

Entity class:

package myapp.domain.myentity;

@Entity
public class MyEntity {

    @Id
    private Long id;

    @Column
    private String comment;

}

Repository interface:

package myapp.domain.myentity;

@Repository
public interface MyEntityRepository extends JpaRepository {

    // EXAMPLE SPRING DATA METHOD
    List findByCommentEndsWith(String x);

    List doSomeHql(Long id);

    List useTheRepo(Long id);

}

Custom methods implementation bean:

package myapp.infrastructure.myentity;

@Component // Must be @Component !!
public class MyEntityRepositoryImpl { // must have the repo name + Impl !!

    @PersistenceContext
    private EntityManager entityManager;

    @Autowired
    private MyEntityRepository myEntityRepository;

    @SuppressWarnings("unused")
    public List doSomeHql(Long id) {
        String hql = "SELECT eFROM MyEntity e WHERE e.id = :id";
        TypedQuery query = entityManager.createQuery(hql, MyEntity.class);
        query.setParameter("id", id);
        return query.getResultList();
    }

    @SuppressWarnings("unused")
    public List useTheRepo(Long id) {
        List es = doSomeHql(id);
        es.addAll(myEntityRepository.findByCommentEndsWith("DO"));
        es.add(myEntityRepository.findById(2L).get());
        return es;
    }

}

The small drawbacks I identified are:

• The custom methods in the Impl class are marked as unused by the compiler, thus the @SuppressWarnings("unused") suggestion.
• You have a limit of one Impl class. (Whereas in the regular fragment interfaces implementation the docs suggest you could have many.)