我如何获得 Spring 数据查询以满足投影中的某些关系（即将集合传递给投影）？

Question

So im trying to make a projection query in spring data. This is my model (in order not to make a huge post with a spam of classes, ill omit constructors, and some annotations):

public class TutorialDAO implements Serializable {
    private UUID id;
    private LocalDateTime created;
    private String createdBy;
    private LocalDateTime lastModified;
    private String lastModifiedBy;
    private int version;
    private boolean exclusive;

    @ManyToMany(mappedBy = "tutorials", cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
    private Set<TopicDAO> topics = new HashSet<>();

    @ElementCollection(fetch = FetchType.EAGER)
    private Set<SectionDAO> sections = new HashSet<>();

    @ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    @JoinTable(name = "tutorial_courses", joinColumns = @JoinColumn(name = "tutorial_id"), inverseJoinColumns = @JoinColumn(name = "course_id"))
    private Set<CourseDAO> courses = new HashSet<>();

    @OneToMany(mappedBy = "tutorial", cascade = { CascadeType.DETACH, CascadeType.MERGE, CascadeType.PERSIST,
            CascadeType.REFRESH }, orphanRemoval = true, fetch = FetchType.EAGER)
    @MapKey(name = "localizedId.locale")
    private Map<String, LocalizableTutorial> localizations = new HashMap<>();

public class TopicDAO implements Serializable {
    private UUID id;
    private String topic;

    @ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
    private Set<TutorialDAO> tutorials = new HashSet<>();
}

public class LocalizedTutorialDAO {
    private UUID id;
    private LocalDateTime created;
    private String createdBy;
    private LocalDateTime lastModified;
    private String lastModifiedBy;
    private int version;
    private boolean exclusive;
    private String name, description;
    private Set<TopicDAO> topics = new HashSet<>();
    private Set<SectionDAO> sections = new HashSet<>();

    public LocalizedTutorialDAO(UUID id, LocalDateTime created, String createdBy, LocalDateTime lastModified,
            String lastModifiedBy, int version, boolean exclusive, String name, String description,
            Set<TopicDAO> topics) {
        super(id, created, createdBy, lastModified, lastModifiedBy, version);
        System.out.println(topics);
        System.out.println();
        this.name = name;
        this.description = description;
        this.topics = topics;
    }
}

Im trying to make a projection query that "fills" the LocalizedTutorialDAO class, which means i want the topics relation for example (same happens with sections, but since its a similar ill just mention topics). I have this @Query annotation:

select new LocalizedTutorialDAO(t.id, t.created, t.createdBy, t.lastModified, t.lastModifiedBy, t.version, t.exclusive, (VALUE(l)).name, (VALUE(l)).description, topics) from tutorial t join t.localizations l join t.topics as topics where (VALUE(l)).name like %:name% and (KEY(l)) = :lang

To clear up, the TutorialDAO object has multi-language support, and my query gets the "normal" variables in TutorialDAO as well as the topics and sections relations. Then it gets the name and description from a given language for example i want to see a tutorial which name has "cooking fish" in portuguese - "pt". Now this part, concerning name and description is working, ive tested it without getting topics and sections and the entity gets populated correctly. My issue here has been ive tried native sql, and spring data non native query and i can never get it to work. Like this, the current query, it says:

org.hibernate.hql.internal.ast.QuerySyntaxException: Unable to locate appropriate constructor on class [com.fullstack.daos.projections.LocalizedTutorialDAO]. Expected arguments are: java.util.UUID, java.time.LocalDateTime, java.lang.String, java.time.LocalDateTime, java.lang.String, int, boolean, java.lang.String, java.lang.String, com.fullstack.daos.TopicDAO [select new com.fullstack.daos.projections.LocalizedTutorialDAO(t.id, t.created, t.createdBy, t.lastModified, t.lastModifiedBy, t.version, t.exclusive, (VALUE(l)).name, (VALUE(l)).description, topics) from com.fullstack.daos.TutorialDAO t join t.localizations l join t.topics as topics where (VALUE(l)).name like :name and (KEY(l)) = :lang]

And if i try the native where instead of putting topic on the constructor i put topic.id, topic.topic it never works always because it says it cant convert TopicDAO to Set. Is there any way to tell hibernate how to do this? For example, the findById() query auto generated by spring works, generating this sql query:

select
        tutorialda0_.id as id1_33_0_,
        tutorialda0_.created as created2_33_0_,
        tutorialda0_.created_by as created_3_33_0_,
        tutorialda0_.last_modified as last_mod4_33_0_,
        tutorialda0_.last_modified_by as last_mod5_33_0_,
        tutorialda0_.version as version6_33_0_,
        tutorialda0_.exclusive as exclusiv7_33_0_,
        localizati1_.id as id1_8_1_,
        localizati1_.locale as locale2_8_1_,
        localizati1_.locale as formula413_1_,
        localizati1_.id as id1_8_2_,
        localizati1_.locale as locale2_8_2_,
        localizati1_.description as descript3_8_2_,
        localizati1_.name as name4_8_2_,
        sections2_.tutorial_id as tutorial1_34_3_,
        sectiondao3_.id as sections2_34_3_,
        sectiondao3_.id as id1_22_4_,
        sectiondao3_.parent_id as parent_i2_22_4_,
        children4_.parent_id as parent_i2_22_5_,
        children4_.id as id1_22_5_,
        children4_.id as id1_22_6_,
        children4_.parent_id as parent_i2_22_6_,
        topics5_.tutorials_id as tutorial2_31_7_,
        topicdao6_.id as topics_i1_31_7_,
        topicdao6_.id as id1_27_8_,
        topicdao6_.topic as topic2_27_8_
    from
        tutorials tutorialda0_
    left outer join
        localized_tutorial localizati1_
            on tutorialda0_.id=localizati1_.id
    left outer join
        tutorials_sections sections2_
            on tutorialda0_.id=sections2_.tutorial_id
    left outer join
        sections sectiondao3_
            on sections2_.sections_id=sectiondao3_.id
    left outer join
        sections children4_
            on sectiondao3_.id=children4_.parent_id
    left outer join
        topics_tutorials topics5_
            on tutorialda0_.id=topics5_.tutorials_id
    left outer join
        topics topicdao6_
            on topics5_.topics_id=topicdao6_.id
    where
        tutorialda0_.id=?

Answer 1

That's not possible with JPQL/HQL constructor expressions or Spring Data Projections as these concepts do not support collections.

I think this is a perfect use case forBlaze-Persistence Entity Views .

I created the library to allow easy mapping between JPA models and custom interface or abstract class defined models, something like Spring Data Projections on steroids. The idea is that you define your target structure(domain model) the way you like and map attributes(getters) via JPQL expressions to the entity model.

A DTO model for your use case could look like the following with Blaze-Persistence Entity-Views:

@EntityView(Tutorial.class)
public interface LocalizedTutorialDAO {
    @IdMapping
    UUID getId();
    LocalDateTime getCreated();
    String getCreatedBy();
    LocalDateTime getLastModified();
    String getLastModifiedBy();
    int getVersion();
    boolean isExclusive();
    @Mapping("localizations[:lang].name")
    @AttributeFilter(ContainsFilter.class)
    String getName();
    @Mapping("localizations[:lang].description")
    String getDescription();
    Set<TopicDAO> getTopics();

    @EntityView(Topic.class)
    interface TopicDAO {
        @IdMapping
        UUID getId();
        String getTopic();
    }
}

Querying is a matter of applying the entity view to a query, the simplest being just a query by id.

LocalizedTutorialDAO a = entityViewManager.find(entityManager, LocalizedTutorialDAO.class, id);

The Spring Data integration allows you to use it almost like Spring Data Projections: https://persistence.blazebit.com/documentation/entity-view/manual/en_US/index.html#spring-data-features

Page<LocalizedTutorialDAO> findAll(Pageable pageable, EntityViewSettingProcessor<LocalizedTutorialDAO> processor);

and use it like:

Page<LocalizedTutorialDAO> p = repo.findAll(pageable, setting -> setting.addAttributeFilter("name", nameParameter));

The best part is, it will only fetch the state that is actually necessary!