Spring Data JPA And NamedEntityGraphs

问题

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);
}

回答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 :(

回答2:

We had the same issue and built a Spring Data JPA extension to solve it :

https://github.com/Cosium/spring-data-jpa-entity-graph

This extension allows to pass named or dynamically built EntityGraph as an argument of any repository method.

With this extension, you would have this method immediatly available:

List<Complaint> findAll(Sort sort, EntityGraph entityGraph);

And be able to call it with an EntityGraph selected at runtime.

回答3:

Use @EntityGraph together with @Query

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

   @EntityGraph(value = "allJoinsButMessages" , type=EntityGraphType.FETCH)
   @Query("SELECT c FROM Complaint ORDER BY ..")
   @Override
   List<Complaint> findAllJoinsButMessages();

   @EntityGraph(value = "allJoins" , type=EntityGraphType.FETCH)
   @Query("SELECT c FROM Complaint ORDER BY ..")
   @Override
   List<Complaint> findAllJoin();

   ...

}

回答4:

Can you try create EntiyGraph name with child that you will request and give same name to the find all method. Ex:

@EntityGraph(value = "fetch.Profile.Address.record", type = EntityGraphType.LOAD)
 Employee getProfileAddressRecordById(long id);

For your case:

@NamedEntityGraph(name="all.Customer.handling_employee.genre", attributeNodes = {
        @NamedAttributeNode("customer"),
        @NamedAttributeNode("handling_employee"),
        @NamedAttributeNode("genre")
})

method name in repository

@EntityGraph(value = "all.Customer.handling_employee.genre" , type=EntityGraphType.FETCH)
 findAllCustomerHandlingEmployeeGenre

This way you can keep track of different findAll methods.

来源：https://stackoverflow.com/questions/31943989/spring-data-jpa-and-namedentitygraphs

标签

jpa

fetch

spring-data-jpa

entitygraph