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Summary:

CoreData throws an Exception when removing NSCollectionView Items and saving while NSCollectionView is performing it's animation.

Project setup/environment: CoreData model with two entities: "Item" and "RelatedItem". "Item" has a relation to "RelatedItem". Both entities each contain two attributes: "foo" and "bar" (NSString), which are bound to the view (NSCollectionViewItem).

Steps to Reproduce:

Open attached Project or clone at https://github.com/artifacts/NSCollectionViewCoreDataBug
Hit "Add" button a couple of times. Some items will be added.
Save document under an arbitrary name.
Start clicking "Remove"-Button a couple of times and WHILE NSCollectionView IS ANIMATING hit Cmd-S to save.
Expected Results:

The document should be saved without error.

Actual Results:

CoreData could not fulfill a fault for '0x1001f40b0 x-coredata://64DE7FCC-8F74-4445-8F6F-173ECA2CB5C4/Item/p5'

Regression:

This also happens in undo/redo scenarios. E.g.: Add some items, save, remove all items, save again, undo until no more undo possible, redo, CRASH:

2011-08-05 12:28:01.942 CollectionViewCoreDataBug[73308:a0f] CoreData could not fulfill a fault for '0x1004e73a0 x-coredata://0F566CD9-715B-46EB-8E2F-66EF9CA08869/Item/p1' 2011-08-05 12:28:02.493 CollectionViewCoreDataBug[73308:a0f] CoreData could not fulfill a fault for '0x10047fc30 x-coredata://0F566CD9-715B-46EB-8E2F-66EF9CA08869/RelatedItem/p4' 2011-08-05 12:28:02.587 CollectionViewCoreDataBug[73308:a0f] Cannot remove an observer for the key path "relatedItem.bar" from , most likely because the value for the key "relatedItem" has changed without an appropriate KVO notification being sent. Check the KVO-compliance of the NSManagedObject class. 2011-08-05 12:28:02.598 CollectionViewCoreDataBug[73308:a0f] Serious application error. Exception was caught during Core Data change processing: CoreData could not fulfill a fault for '0x10047fc30 x-coredata://0F566CD9-715B-46EB-8E2F-66EF9CA08869/RelatedItem/p4' with userInfo { NSAffectedObjectsErrorKey = ( " (entity: RelatedItem; id: 0x10047fc30 x-coredata://0F566CD9-715B-46EB-8E2F-66EF9CA08869/RelatedItem/p4 ; data: )" ); }

This also happens on Lion.

Notes:

I'm not alone, see:

http://stackoverflow.com/questions/4733911/is-nscollectionview-compatible-with-coredata/6951079#6951079