Core data mapping model with new (non-optional) relationship

Question

My original data model has an entity "Game". I have now updated the model to include an entity, "Match", which can refer to multiple games. I wish to add a Match to all of my old Games, and ideally this would be a non-optional relationship.

Currently I am setting Match to be optional, and simply adding a Match to every old Game in application:didFinishLaunching after the model has been updated. This works, but I'm wondering if this is really the best way to do it.

I have tried to follow the tutorial here, but I am getting stuck on the part with "StepOneEntityMigrationPolicy.m". I have created an NSEntityMigrationPolicy subclass and set it in the mapping model. I've tried overriding both createDestinationInstancesForSourceInstance and createRelationshipsForDestinationInstance:, but neither get called.

Is this perhaps because my Source and Destination are both the same (GameToGame)? Also, is there any benefit to doing this via the mapping model rather than as I am doing it now?

Answer 1

I think the simplest and most pragmatic way is what you are doing now, i.e. inserting the necessary new entities "manually" after an update. This is a common way to populate orphaned entities after a model version upgrade and perfectly fine.