[java] How to add custom method to Spring Data JPA

There's a slightly modified solution that does not require additional interfaces.

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

• Define in you regular @Repository interface, say MyEntityRepository the custom methods (in addition to your Spring Data 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 (for completeness):

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<MyEntity, Long> {

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

    List<MyEntity> doSomeHql(Long id);   // custom method, code at *Impl class below

    List<MyEntity> useTheRepo(Long id);  // custom method, code at *Impl class below

}

Custom methods implementation bean:

package myapp.infrastructure.myentity;

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

    @PersistenceContext
    private EntityManager entityManager;

    @Autowired
    private MyEntityRepository myEntityRepository;

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

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

}

Usage:

// You just autowire the the MyEntityRepository as usual
// (the Impl class is just impl detail, the clients don't even know about it)
@Service
public class SomeService {
    @Autowired
    private MyEntityRepository myEntityRepository;

    public void someMethod(String x, long y) {
        // call any method as usual
        myEntityRepository.findByCommentEndsWith(x);
        myEntityRepository.doSomeHql(y);
    }
}

And that's all, no need for any interfaces other than the Spring Data repo one you already have.

The only possible 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.)
• If you place the Impl class at a different package and your test uses only @DataJpaTest, you have to add @ComponentScan("package.of.the.impl.clazz") to your test, so Spring loads it.