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JOIN FETCH in spring-data-jpa does not fetch lazy associations


By : Алексей Сукач
Date : October 16 2020, 06:10 AM
I wish this help you Yes, unidirectional mapping should work. I am not having any problem with a basic example of what you are doing. This should be a good starting point to help you figure out what the differences are. I notice that I don't join movie.users in the countQuery.
code :
@Entity
public class Movie {
    @Id @GeneratedValue private Long id;
    @ManyToMany
    private Set<Genre> genres;
    @ManyToMany
    private Set<User> users;

@Entity
public class Genre {
    @Id @GeneratedValue private Long id;        
    @ManyToMany
    private Set<User> users;

@Entity
public class User {
    @Id @GeneratedValue private Long id;
public interface MovieRepository extends JpaRepository<Movie, Long> {
    @Query(value = "SELECT movie FROM Movie movie " +
            "JOIN movie.genres genres JOIN genres.users users LEFT JOIN FETCH movie.users " +
            "WHERE users.id = :userId", 
    countQuery = "SELECT COUNT(movie) FROM Movie movie " +
            "JOIN movie.genres genres JOIN genres.users users " +
            "WHERE users.id = :userId")
    Page<Movie> getAllMoviesByFavoriteGenres(@Param("userId") Long userId, Pageable page);
@Override
public void run(String... args) throws Exception {
    create();
    System.out.println("something");
    Page<Movie> movies = movieRepo.getAllMoviesByFavoriteGenres(1L, PageRequest.of(0, 10));
    movies.forEach(System.out::println);
}

private void create() {
    User u1 = new User();
    userRepo.save(u1);

    Set<User> users = Collections.singleton(u1);

    Genre g1 = new Genre();
    g1.setUsers(users);
    genreRepo.save(g1);

    Set<Genre> genres = Collections.singleton(g1);

    Movie m1 = new Movie();
    m1.setGenres(genres);
    m1.setUsers(users);
    movieRepo.save(m1);
}


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Fetch data from table using hibernate with fetch=FetchType.LAZY


By : wwwgizy
Date : March 29 2020, 07:55 AM
will be helpful for those in need It seems your service method is not annotated with @Transactional. Thus, after calling userDAO.getUserById(id);, there is no longer a transaction. That means that you cannot access any lazy-loaded properties of the loaded entity that hasn't been accessed/pre-fetched inside the transaction without running into a LazyInitializationException.
So you can either think about replacing LAZY with EAGER fetching (this mostly depends on the use cases you are facing) or you should annotate your Service method with @Transactional.
code :
criteria.setFetchMode("communicationAddresses", FetchMoode.EAGER);

How to avoid lazy fetch in JSON serialization using Spring Data JPA + Spring Web MVC?


By : user19863
Date : March 29 2020, 07:55 AM
This might help you If I understood you properly, you want to serialize only when the lazy loaded collection is fetched, but you don't want the serialization to trigger the fetching.
If that is the case you should use the jackson-datatype-hibernate, and added as their docs already explains
code :
public class HibernateAwareObjectMapper extends ObjectMapper {

    public HibernateAwareObjectMapper() {
        registerModule(new Hibernate4Module());
    }
}
 <mvc:annotation-driven>
        <mvc:message-converters>
            <!-- Use the HibernateAware mapper instead of the default -->
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="path.to.your.HibernateAwareObjectMapper" />
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

Eclipselink fetch-join lazy associations of a subclass


By : Rodrigo Mastropietro
Date : March 29 2020, 07:55 AM

Not able to fetch data with left join and join fetch together in JPQL query with entiy graphs as a hint


By : user2326717
Date : March 29 2020, 07:55 AM
will help you I am using Jpa 2.2 with Hibernate 5.3.7 final jar. Below are my entities and code for the test case is not executing correctly:
code :
  Below code fetches Only those instrcutors having IdProof present in
  DB . If No Instructor is having idProof present in db then written
  query will return empty List as there is inner join between
  Instructor and IdProof . 

  All Instructors not having any vehicle will also be fetched and their
  vehicle list  will be initialised as empty.

  All vehicle not having any document will also be fetched along with
  vehicles having atleast one document . Vehicles not having any
  document can be avoided in code while processing data . 

  But if inner join is created between Vehicle and document and if
  there is no  document present in db then it will make the complete
  result empty . As final inner join will be applied on join results
  evaluted till yet in db on first three tables Instructor , IdProof and 
  Vehcile.


    try {
       TypedQuery<Instructor> 
       typedQueryLeftJoinAndJoinFetchMixed = 
       em.createQuery(" select i from Instructor i "
               + " join fetch i.idProof id " 
               + " left join i.vehicles v " 
               + " left join v.documents vd ",
                    Instructor.class);
       typedQueryLeftJoinAndJoinFetchMixed.
                   setHint("javax.persistence.fetchgraph", instructorGraph);
       List<Instructor> 
           instructorsWithLeftJoinAndJoinFetchMixed = 
                               typedQueryLeftJoinAndJoinFetchMixed
                                        .getResultList();
                            } catch (Exception e) {
                                e.printStackTrace();
                            }

                        }

Fetch lazy object while serializing in spring data rest


By : mgsesq
Date : March 29 2020, 07:55 AM
I wish did fix the issue. In order to have nested related objects in the output JSON you have to use projections.
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