I need to know the type of return that Spring JPA returns to put in the Service package, because it is giving NullPointerException :
Dao:
public interface PlaylistDao extends JpaRepository<Playlist, Long> {
@Query("select count(*) from Playlist")
public int verifica();
}
Service:
@Service
@Transactional
public class PlaylistServiceImpl implements PlaylistService {
@Autowired
private PlaylistDao dao;
public int verifica(){
return dao.verifica();
}
}
The interface JpaRepository (which inherits from CrudRepository ) already comes with a method ready for this action.
It is called count() and returns long .
Instead of declaring a new method, you can use this one.
See the documentation for more information. .
It returns a Long, due to its count.
TypedQuery<Long>
You can use the Spring JPA Repository notation to do count , as igventurelli said:
public interface PlaylistDao extends JpaRepository<Playlist, Long> {
long count();
}
If you want to count some attribute of the entity, simply add the
long countByName();
If you want to make a count more complex, which involves @Query , you can do:
@Query("SELECT count(*) FROM Playlist")
long countPlaylist();
If you want to use Entity Manager with the following Jpql:
String jpql = "SELECT COUNT(*) FROM Playlist");
You can use TypedQuery<Long >:
TypedQuery<Long> query = entityManager.createQuery(jpql , Long.class);
long total = query.getSingleResult();
Or Number :
Query queryCount = entityManager.createQuery(jpql);
long total = ((Number) queryCount.getSingleResult()).longValue();
To read the final result.