JPA将实体的“多对多”字段值替换为其他值

Question

I have an Entity called Artwork which has a member called subjects mapped Many to Many with another entity as follows.

@ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<ArtSubject> subjects;

Assume that in my Artwork table i have a record with subjects values as (ArtSubject1, ArtSubject2, ArtSubject3)

I have to replace this value with (ArtSubject5, ArtSubject6, ArtSubject7) .

Completely different List.

Curretly if i save an Artwork object with new data as (ArtSubject5, ArtSUbject6, ArtSubject7) .

JPA appends it with the already existing list and the resulting data is (ArtSubject1, ArtSubject2, ArtSubject3, ArtSubject5, ArtSUbject6, ArtSubject7)

I want it to be only (ArtSubject5, ArtSubject6, ArtSubject7)

Please find the method where i save the ArtSubject and set it to the Artwork object.

ArtWork artwork = new ArtWork();
        List<ArtSubject> subject = new ArrayList<>();
        List<ArtStyle> style = new ArrayList<>();
        Artist artist = new Artist();
        List<ArtCollection> artCollections = new ArrayList<>();

        // Classifying Collections into each category.
        for (Collection collection : collections) {
            String tokens[] = collection.getTitle().split("_");
            if (tokens == null || tokens.length < 2) {
                LOGGER.info("Invalid Collection Type: Collection type {} not recognised", 
                        collection.getTitle());
                continue;
            }
            String collectionType = tokens[0]; 
            switch(collectionType) {
            case "subject":
                ArtSubject artSubject = new ArtSubject(collection.getId(), 
                        collection.getTitle().split("_")[1]);
                subject.add(artSubject);
                artSubjectRepository.save(artSubject);
                break;
            default:
                LOGGER.info("Invalid Collection Type: Collection type {} not recognised", 
                        collection.getTitle());
                break;
            }
        }


        artwork.setSubject(subject);

After this i save the artwork as artRepository(CRUD Repository) artRepository.save(artwork) Please help me with this.

Thanks in advance!

Answer 1

Try below approaches

For Collection(List) ( artwork.setSubjects(new ArrayList<Subject>()); ) you have to clear() the existing one. This happens because if Hibernate loads the entity (and its collections) from DB, it "manages" them, ie. tracks their changes. Generally when using Hibernate it's better not to create any setters for collections (lists, sets) . Create only the getter, and clear the collection returned by it, ie:

artwork.getSubject().clear();

Also, use orphan deletion (ie. delete child object when it's removed from collection in the parent). Add @OneToMany(orphanRemoval=true) in owning entity.

Answer 2

Try this, I am trying to save a person which has oneToMany relationship too...I just use saveOrUpdate, and in frontend even if person edits his details, I call the same method :

@Override
    @Transactional
    public void addPerson(Person p) {

        if( session == null) {
            session = this.sessionFactory.openSession();
        }else {
            session = this.sessionFactory.getCurrentSession();
        }
        session.saveOrUpdate(p);
        session.flush();

    }

For saving the entity mapped with one-to-many, i do it this way : here alsso, if canvas details are changed, it does not matter, I call the same method.

@Override
public void addCanvas(Canvas canvas, Person person) {
    int id = person.getId();
    if( session == null) {
        session = this.sessionFactory.openSession();
    }else {
        session = this.sessionFactory.getCurrentSession();
    }
    Person person1 = (Person) session.get(Person.class,id);
    person.getCanvas1().add(canvas);
    canvas.setPerson1(person1);
   session.merge(canvas);

    session.flush();
}