NSManagedObject+extension.swift

public extension NSManagedObjectContext {
    
    func addContextDidSaveNotificationObserver(center: NSNotificationCenter, handler: NSNotification -> ()) -> NSObjectProtocol {
        return center.addObserverForName(NSManagedObjectContextDidSaveNotification, object: self, queue: nil) { notification in
            handler(notification)
        }
    }
    
    func performMergeChangesFromContextDidSaveNotification(notification: NSNotification) {
        self.performBlock {
            self.mergeChangesFromContextDidSaveNotification(notification)
            guard let updatedObjects = notification.userInfo?[NSUpdatedObjectsKey] as? Set<NSManagedObject> else {
                return
            }
            updatedObjects.map({ $0.objectID }).forEach { objectID in
                guard let object = try? self.existingObjectWithID(objectID) else {
                    return
                }
                self.refreshObject(object, mergeChanges: false)
            }
        }
    }
}

// Prototype of a CoreDataStack class to illustrate how you could use the `NSManagedObjectContext` extension methods
class CoreDataStack {
    var mainContext: NSManagedObjectContext
    var backgroundContext: NSManagedObjectContext
    
    var backgroundObserver: NSObjectProtocol?
    
    deinit() {
        if let backgroundObserver = self.backgroundObserver {
            NSNotificationCenter.defaultcenter().removeObserver(backgroundObserver)
        }
    }
    
    init() {
        //....  
        // A bunch of initialization code here where you define backgroundContext and mainContext
        //....
        
        // Somewhere else in your code you would register your main context to listen to `NSManagedObjectDidChangeNotification` 
        // coming from the background context like so
        backgroundObserver = backgroundContext.addContextDidSaveNotificationObserver(
            NSNotificationCenter.defaultcenter(),
            handler: processBackgroundContextDidSaveNotification
        )
    }

    private func processBackdroundContextDidSaveNotication(notification: NSNotification) {
        mainContext.performMergeChangesFromContextDidSaveNotification(notification)
    }
}