Lightweight migration of existing core data database with iCloud to iOS 7

Question

The WW2013 video on Core Data & iCloud mentioned that pre-iOS7 core data storage with iCloud can be migrated to the iOS7 way by specifying the NSPersistentStoreUbiquitousContentURLKey when setting up your persistent store coordinator.

Has anyone had any luck with this? With my persistent store, I had the SQLLite database in a .nosync folder and my log files in a different subdirectory. I've tried setting the NSPersistentStoreUbiquitousContentURLKey to point to each and I always get my entire database being over-written instead of everything migrating over.

Answer 1

I don't recall anything being said about migrating to iOS 7, I recall them indicating that to maintain compatibility with legacy apps where a custom path was specified for transaction logs you can continue using the NSPersistentStoreUbiquitousContentURLKey. This key should only be used to point to the log directory and nothing gets migrated when you use this, Core Data just uses the existing store and iCloud transaction logs.

To migrate it so that it uses the new defaults in iOS7 you would need to use the migratePersistentStore API to create a new store using a new file URL and only the NSPersistentStoreUbiquitousContentNameKey. Core Data will then automatically create the fallback and local (iCloud synced) store and iCloud transaction log files for you.

EDIT:

If anyone else is trying this an having problems try setting the store to use JOURNAL mode rather than the new default WAL mode. There seem to be some issues when doing certain migrations while using WAL mode. If anyone has figured out whether WAL mode has specific bugs please add a link here.