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Collection of error messages using Core Data and what caused them (including incorrect bindings). Feel free to add your own - hopefully next time you see one of these, this will remind you why. See also CoreDataBindingsProblems - PaulCollins

If you find this page useful, please file bugs on these issues so Apple makes it easier to use Core Data. Cut and Paste if you like.

Non-error problems

Error Messages with Unknown Causes (Requests for Help)

The document “Untitled” could not be saved. Could not merge changes. I was having a problem where I was getting this error every time I modified any data. It didn’t occur with NSBinaryStoreType or NSXMLStoreType but it happened every time with NSSQLiteStoreType. Also I was forcing the app to open the document with openDocumentWithContentsOfURL and forcing the type inside configurePersistentStoreCoordinatorForURL.

It turns out that somehow the framework gets confused if the document you open with openDocumentWithContentsOfURL has a file extension that doesn’t match that you’ve specified in your Info.plist’s CFBundleTypeExtensions. I don’t see why this should be a problem since it correctly opened the document anyway, it just bombs when trying to modify it and save it again. So the error message has no apparent relation to the cause. *