Core Data migration of to-one relationship to to-many relationship?

That migration should be easy enough that automatic migration will work. Worst case is that it would require a mapping model but I suspect it will "just work" by turning on auto migration.

I ended up needing to subclass NSEntityMigrationPolicy several times. This was necessary because properties were moving from/to different entities with several levels of abstraction being added to support a considerably more general model. Also important was the ordering of entity mappings within the mapping model.

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