If you extend NSManagedObject or you use a static method to instantiate your Model class or you set your NSPersistentStoreCoordinator type to NSInMemoryStoreType will your NSValueTransformer class still execute?
The answer was if the persistent store type is set to NSInMemoryStoreType your NSValueTransformer that you setup in Core Data will not get executed.
Hope this helps someone. If you find this in any doc or have an answer why this is so please post it here.