Objectbox-java: Support to many-to-many relationships

[daividssilverio]

I've tried to create simple many-to-many relationship using a auxiliary object, but it didn't work.

@Entity
public class Owner {
    @Id long id;

    @Relation(idProperty = "ownerId")
    List<PetOwner> pets;
}


@Entity
public class Pet {
    @Id long id;

    @Relation(idProperty = "petId")
    List<PetOwner> owners;
}

@Entity
public class PetOwner {
    @Id long id;

    long petId;
    long ownerId;

    @Relation Owner owner;
    @Relation Pet pet;
}

When I compile my project. I get this code generated:

// THIS CODE IS GENERATED BY ObjectBox, DO NOT EDIT.

/**
 * Cursor for DB entity "Owner".
 */
public final class OwnerCursor extends Cursor<Owner> {

    private static Properties PROPERTIES = new Owner_();


    // Property IDs get verified in Cursor base class

    public OwnerCursor(Transaction tx, long cursor) {
        super(tx, cursor, PROPERTIES);
    }

    @Temporary
    public OwnerCursor() {
    }

    @Override
    public final long getId(Owner entity) {
        return entity.getId();
    }

    /**
     * Puts an object into its box.
     *
     * @return The ID of the object within its box.
     */
    @Override
    public final long put(Owner entity) {
       //**----->>>> MISSING RETURN STATEMENT**
    }

    // TODO @Override
    protected final void attachEntity(Owner entity) {
        // TODO super.attachEntity(entity);
        entity.__boxStore = boxStoreForEntities;
    }

    // TODO do we need this? @Override
    protected final boolean isEntityUpdateable() {
        return true;
    }

I've tried to do something simpler, but it's not supported yet, as said in the documentation:

Something like

@Entity
public class Pet {
   @Id long id;
   @Relation
    List<Owner> owners;
}

@Entity
public class Owner {
    @Id long id;
    @Relation
    List<Pet> pets;
}

would be much nicer, I think.

[greenrobot]

This will be supported very soon in upcoming 0.9.8 (if plans do not change).

Side note: I would have expected a pet to have a single owner. This is fully supported right now.

[daividssilverio]

Nice!

But the missing return statement I mentioned, wasn't something supposed to be there right now, or did I try to do something not supported yet?

PS: But that's why sometimes people go to court to decide who gets to keep the dog, cat, whatever, after a divorce. :c Anyway, I was just testing.

[greenrobot]

The put() method of Owner was just empty?

[daividssilverio]

Yup

On Mon, Jan 30, 2017, 08:55 greenrobot [e-mail] wrote:

The put() method of Owner was just empty?

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[brussee]

@greenrobot How are M:N relations currently supported amoungst 1 single class?

My use case is @Entity class Person with typically 2 parents and 1..* children, all class Person objects.

Does this require an @Entity class ParentChildRelation with long parentId and long childId to make this work?

18

[greenrobot]

FYI: We are currently working on this. First step will be standalone to-many relations. In the future we will expand this with backlinks (which will enable M:N; until then you could workaround with two to-many relations).

[greenrobot]

One-way to-many relations were introduced in ObjectBox 0.9.14. Backlinks to those will come at a later release (rather soon-ish).

[jpmcosta]

Do you have any milestone to add Backlinks for many-to-many relationships?

[greenrobot]

@jpmcosta We need to prioritize feature requests. Would you be available for a quick chat? Please send us a line using contact at objectbox dot IO. Thank you!

[dgandhi17]

@greenrobot Any update on this ? by when it will be released

[greenrobot-team]

Tracking support for to-many relations with backlink in #407.

This ticket is assigned a milestone for the release of one-way to-many. As that already happened, closing. -ut