Greetings, I was trying to set up automatic migration, and did this brain-o, which will be obvious to most folks, but stumped me for a little bit: psc_options = { NSMigratePersistentStoresAutomaticallyOption:NSNumber.numberWithBool(true), NSInferMappingModelAutomaticallyOption:NSNumber.numberWithBool(true) } fail(error) unless@persistentStoreCoordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration:nil, URL:url, options:psc_options, error:error) When what I should have been doing was something like: psc_options = {} psc_options[NSMigratePersistentStoresAutomaticallyOption] = NSNumber.numberWithBool(true) psc_options[NSInferMappingModelAutomaticallyOption] = NSNumber.numberWithBool(true) ... ...or even... psc_options = { NSMigratePersistentStoresAutomaticallyOption => NSNumber.numberWithBool(true), NSInferMappingModelAutomaticallyOption => NSNumber.numberWithBool(true) } It's subtle bugs like these that make me slap my head... ...but now Core Data automatic migration works! W00t! -- Morgan p.s. If you're trying to do Core Data migration, I found this article particularly useful: http://www.timisted.net/blog/archive/core-data-migration/