Question

I have two entities:

ResourceFile:

@Entity
@Table(name = "resource_file")
public class ResourceFile extends IdEntity<Integer> {

    @Id
    @SequenceGenerator(name = "resource_file_id_generator", sequenceName = "resource_file_id", allocationSize = 1)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "resource_file_id_generator")
    @Column(name = "id", unique = true, nullable = false)
    @Nonnegative
    private Integer id;

    ...
}

FavoriteResourceFile:

@Entity
@Table(name = "favorite_resource_file")
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class FavoriteResourceFile extends IdEntity<FavoriteResourceFileId> {

    @EmbeddedId
    private FavoriteResourceFileId id;

    @MapsId("resourceFileId")
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "resource_file_id", nullable = false)
    private ResourceFile resourceFile;

    ...

}

And I want to make the following query “select all resource files and sort them by favourite resource file’s count”.

In SQL it looks like:

select rf.id, count(frf.resource_file_id) from resource_file rf
left join favorite_resource_file frf on frf.resource_file_id = rf.id
group by rf.id
order by count(rf.id) desc;

But I can’t understand how to do it with Spring Data and how to make mapping to ResourceFile entity at the end.

Some limitations:

• I can’t make relation to FavoriteResourceFile in ResourceFile,
  because they are located in different modules
• I don’t want to use native SQL or JPA query (as strings).
• It’ll be preferable to use Meta-models, Specification or QueryDSL, because they are already used in project.

Can someone help me?

Answer 1

You can use your custom repository implementation along with Crud/PagingAndSorting repository implementation, like this:

End-point repo:

public interface ResourceFileRepository extends
    PagingAndSortingRepository<ResourceFile, Integer>,
    ResourceFileRepositoryCustom {
}

Custom repo:

public interface ResourceFileRepositoryCustom {
    List<ResourceFile> getResourceFilesOrderByFavourites();
}

Custom repo implementation with actual code to retrive ResourceFile’s ordered by favourite count (notice it is ResourceFileRepositoryImpl and not ResourceFileRepositoryCustomImpl).

I didn’t have those embeded keys, so I had to simplify it a little bit.
The query is going FROM the FavoriteResourceFile, because ResourceFile don’t have own relation to FavoriteResourceFile.

public class ResourceFileRepositoryImpl implements ResourceFileRepositoryCustom {
    @PersistenceContext
    private EntityManager em;

    public void setEntityManager(EntityManager em) {
        this.em = em;
    }

    @Override
    public List<ResourceFile> getResourceFilesOrderByFavourites() {
        CriteriaBuilder criteriaBuilder = this.em.getCriteriaBuilder();
        CriteriaQuery<ResourceFile> q = criteriaBuilder
                .createQuery(ResourceFile.class);
        Root<FavoriteResourceFile> root = q.from(FavoriteResourceFile.class);
        Join<FavoriteResourceFile, ResourceFile> join = root.join(
                 FavoriteResourceFile_.resourceFile, JoinType.LEFT);
        q.select(join);
        q.groupBy(join.get(ResourceFile_.id));
        q.orderBy(criteriaBuilder.desc(
                      criteriaBuilder.count(
                          join.get(ResourceFile_.id))));

        TypedQuery<ResourceFile> query = this.em.createQuery(q);
        return query.getResultList();
    }
}

To see full example project (with some very basic sql and test) – checkout/fork/etc:
https://github.com/rchukh/StackOverflowTests/tree/master/13669324