NSFetchedResultsController+extension-additions.swift

extension NSFetchedResultsController {
    private func processChangesWithWillAccessValueForKey(notification: NSNotification) {
        guard let _ = self.fetchRequest.predicate, _ = self.fetchRequest.entity else {
            return
        }
        var matchingObjectIDs = self.insertedOrUpdatedObjectIDsMatchingFetchRequestInNotification(notification)
        self.managedObjectContext.performBlock({
            let registeredObjectIDs = self.managedObjectContext.registeredObjects.map{$0.objectID}
            matchingObjectIDs.subtractInPlace(registeredObjectIDs)
            for matchingObjectID in matchingObjectIDs {
                guard let object = try? self.managedObjectContext.existingObjectWithID(matchingObjectID) else {
                    continue
                }
                object.willAccessValueForKey(nil)
            }
            if !matchingObjectIDs.isEmpty {
                self.managedObjectContext.mergeChangesFromContextDidSaveNotification(notification)
            }
        })
    }
}