Core Data migration fails for to-one relationship

Question

I have the following model:

parent is a to-one relationship (optional, no minimum, maximum=1). children is the inverse to-many relationship (optional, no minimum, no maximum).

I added a new model version, where only the Entity Room is renamed to Classroom, all other entities are unchanged:

I also created a mapping model for the migration, but the migration fails with the error message

reason = "Can't find mapping model for migration";

The strange thing is that if the parent relationship is created with minimum=1 (instead of no minimum) then the migration works without problems.

The persistent store is opened with the options

NSDictionary *options = @{NSMigratePersistentStoresAutomaticallyOption:@YES, NSInferMappingModelAutomaticallyOption:@NO};

Mezzanine

Answer 1

Why do you need a mapping model? You should avoid these complexities and simply use Lightweight Migration as explained in Apple's Lightweight Migration Documentation.

Wallflower

The model is a reduced example of my actual model, which is more complicated and has more changes which don't work with lightweight migration. I just tried to reduce the problem as far as possible – Mezzanine

Then your info about the model change is misleading. Please post the change that you need custom migration for. – Wallflower