fetch - Spring Data JPA And NamedEntityGraphs

Question

currently I am wrestling with being able to fetch only the data I need. The findAll() method needs to fetch data dependant on where its getting called. I do not want to end up writing different methods for each entity graph. Also, I would avoid calling entitymanagers and forming the (repetitive) queries myself. Basicly I want to use the build in findAll method, but with the entity graph of my liking. Any chance?

@Entity
@Table(name="complaints")
@NamedEntityGraphs({
    @NamedEntityGraph(name="allJoinsButMessages", attributeNodes = {
            @NamedAttributeNode("customer"),
            @NamedAttributeNode("handling_employee"),
            @NamedAttributeNode("genre")
    }),
    @NamedEntityGraph(name="allJoins", attributeNodes = {
            @NamedAttributeNode("customer"),
            @NamedAttributeNode("handling_employee"),
            @NamedAttributeNode("genre"),
            @NamedAttributeNode("complaintMessages")
    }),
    @NamedEntityGraph(name="noJoins", attributeNodes = {

    })
})
public class Complaint implements Serializable{
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    private long id;

    private Timestamp date;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "customer")
    private User customer;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "handling_employee")
    private User handling_employee;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="genre")
    private Genre genre;

    private boolean closed;

    @OneToMany(mappedBy = "complaint", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    private List<ComplaintMessage> complaintMessages = new ArrayList<ComplaintMessage>();

//getters and setters
}

And my JPARepository

@Repository
public interface ComplaintRepository extends JpaRepository<Complaint, Long>{

    List<Complaint> findByClosed(boolean closed);

    @EntityGraph(value = "allJoinsButMessages" , type=EntityGraphType.FETCH)
    @Override
    List<Complaint> findAll(Sort sort);
}

Answer 1

We ran into a similar problem and devised several prospective solutions but there doesn't seem to be an elegant solution for what seems to be a common problem.

1) Prefixes. Data jpa affords several prefixes (find, get, ...) for a method name. One possibility is to use different prefixes with different named graphs. This is the least work but hides the meaning of the method from the developer and has a great deal of potential to cause some non-obvious problems with the wrong entities loading.

@Repository
@Transactional
public interface UserRepository extends CrudRepository<User, Integer>, UserRepositoryCustom {
    @EntityGraph(value = "User.membershipYearsAndPreferences", type = EntityGraphType.LOAD)
    User findByUserID(int id);

    @EntityGraph(value = "User.membershipYears", type = EntityGraphType.LOAD)
    User readByUserId(int id);
}

2) CustomRepository. Another possible solutions is to create custom query methods and inject the EntityManager. This solution gives you the cleanest interface to your repository because you can name your methods something meaningful, but it is a significant amount of complexity to add to your code to provide the solution AND you are manually grabbing the entity manager instead of using Spring magic.

interface UserRepositoryCustom {
    public User findUserWithMembershipYearsById(int id);
}

class UserRepositoryImpl implements UserRepositoryCustom {
    @PersistenceContext
    private EntityManager em;
    @Override
    public User findUserWithMembershipYearsById(int id) {
        User result = null;
        List<User> users = em.createQuery("SELECT u FROM users AS u WHERE u.id = :id", User.class)
                .setParameter("id", id)
                .setHint("javax.persistence.fetchgraph", em.getEntityGraph("User.membershipYears"))
                .getResultList();
        if(users.size() >= 0) {
            result = users.get(0);
        }
        return result;
    }
}

@Repository
@Transactional
public interface UserRepository extends CrudRepository<User, Integer>, UserRepositoryCustom {
    @EntityGraph(value = "User.membershipYearsAndPreferences", type = EntityGraphType.LOAD)
    User findByUserID(int id);
}

3) JPQL. Essentially this is just giving up on named entity graphs and using JPQL to handle your joins for you. Non-ideal in my opinion.

@Repository
@Transactional
public interface UserRepository extends CrudRepository<User, Integer>, UserRepositoryCustom {
    @EntityGraph(value = "User.membershipYearsAndPreferences", type = EntityGraphType.LOAD)
    User findByUserID(int id);

    @Query("SELECT u FROM users WHERE u.id=:id JOIN??????????????????????????")
    User findUserWithTags(@Param("id") final int id);
}

We went with option 1 because it is the simplest in implementation but this does mean when we use our repositories we have have to look at the fetch methods to make sure we are using the one with the correct entity graph. Good luck.

Sources:

• JPA EntityGraph with different views using Spring
• https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#repositories.query-methods

I don't have enough reputation to post all of my sources. Sorry :(