How to persist n:n releated entities programmatically

Support
#1

How to set and persist a n:n relation?
E.g.:
Car car= metadata.create(Car.class);
car.getInstalledSystems().Add(…) // this doesnt work because the related set (InstalledSystems) is Null

Must the releated entities set be instantiated (e.g. by calling setInstalledSystems(…))? How to persist the relations with entitymanager?

#2

Yes, when creating to-many associations programmatically (not using client-tier datasources), you should instantiate collections:


Car car = metadata.create(Car.class);
car.setInstalledSystems(new HashSet());
car.getInstalledSystems().add(x);
car.getInstalledSystems().add(y);
car.getInstalledSystems().add(z);
persistence.getEntityManager().persist(car);

The relation will be saved together with car if the car entity has an owning side of relation (for many-to-many relations generated by Studio both sides are owning). The x,y,x instances should be either detached (already exist in the database), or persisted in the same transaction.