Get only selected data from JPA query - jpa

Question

I cound't find any nice solution to get only selected data from the domain?
E.g I have class:
#Entity
public class Reservation {
// private Integer RESERVATION_ID;
// private Integer id;
private long code;
private Date date;
private Client reservationClient;
private WashType reservationWashType;
private Vehicle reservationVehicle;
private Wash reservationWash;
private Worker reservationWorkerPesel;
private Review reservationReview;
private ReservationReminder reservationReminder;
}
And have simple query repository
public interface ReservationRepository extends JpaRepository<Reservation, Long> {
Reservation findByCode(long code);
}
I'd like to take from that query the Reservation object but without data's from class like Review, Worker.
So it means my result should looks like:
a whole object of Reservation which includes:
code,date,Client reservationClient,WashType reservationWashType,Vehicle reservationVehicle,Wash reservationWash, ReservationReminder reservationReminder
Is it possible to exclude it in nice way? Or if not how can I manage it?

Answer 1

Yes, you can easily do that so long as Review and Worker are marked to be lazily loaded.
What I mean is:
#ManyToOne(fetch = FetchType.LAZY)
private Review review;
Hibernate won't attempt to load the Review association until you call #getReview().
For situations then where you want your Reservation with the Review, you would then just need to specify at query-time that you want the relationship join-fetched.
#Query("SELECT r FROM Reservation r JOIN FETCH r.review WHERE r.code = :code")
List<Reservation> findByCode(Long code);
Remember, if Review cannot be null, make sure that #ManyToOne has the optional=false attribute so that when the join gets generated, it uses an inner join rather than an outer join to avoid performance overhead.