在完成处理程序中尝试更新时，CoreData提取的对象变为零-Swift4

Question

        let bgContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)

        let moc = appDelegate.coreData.persistentContainer.viewContext
        bgContext.parent = moc
        bgContext.perform({

            let fetchedResultController: NSFetchedResultsController<ReservationsEntity>
            let request: NSFetchRequest<ReservationsEntity> = ReservationsEntity.fetchRequest()
            let sort = NSSortDescriptor(key: #keyPath(ReservationsEntity.reservedDate), ascending: true)
            request.sortDescriptors = [sort]
            request.predicate = NSPredicate(format: "isSynced == %@", NSNumber(value: false))
            fetchedResultController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: moc, sectionNameKeyPath: nil, cacheName: nil)

            do{
                try fetchedResultController.performFetch()
                for reservationEntity in fetchedResultController.fetchedObjects!{

                    print(reservationEntity.isSynced!)
                    let params = BaseViewController.getReservationDictionaryForOffline(reservation: reservationEntity)
                    ServerCalls.addReservationToServer(parametersForReservation: params, kindOfScreen: 0, completionHandler: { (response) in
                        print(reservationEntity.isSynced!)

                        reservationEntity.isSynced = true

                    })
                }

            } catch{

            }


        })

Issue : Hello!I have a use case saying AddReservation where I add a record to CoreData Entity named ReservationsEntity with an attribute isSynced to false initially. I also make a server call simultaneously and once the server call returns, I am trying to update the flag isSynced to true . But after the server call returns my CoreData object is becoming nil.

As per the code posted above, first print(reservationEntity.isSynced!) shows false in the debugger. When I try to print/ access reservationEntity after ServerCalls.addReservationToServer returns, app crashes as the reservationEntity object becomes nil .

I have been trying to fix it for the past few days trying different ways but of no use. What's the mistake I am doing here?

Answer 1

Can you try this code

let bgContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
bgContext.persistentStoreCoordinator = appDelegate.coreData.persistentContainer.persistentStoreCoordinator

And remove

let moc = appDelegate.coreData.persistentContainer.viewContext
bgContext.parent = moc