Application crashes when saving in CoreData concurrently in Swift - swift

Question

Application crashes when saving in Core data
do {
try context.save() <----------- CRASH ---------
} catch {
print("Failed saving")
}
I save data in Core data in background using this code
DispatchQueue.global(qos: .background).async {
// Fetches from database
DispatchQueue.main.async {
if fetchedActivitiesFromDB {
// Updates the view
} else {
// gets from the server
// Save the result in Core Data <------------
let coreData = CoreDataHelper()
coreData.saveInDB(fetchedItemsFromServer)
}
}
}
According to above code this is possible to save in CoreData concurrently.
I did some tasks to resolve the problem but they didn't work.
First: I wanted to create a queue in order to handle concurrent save
let saveQueue = DispatchQueue(label: "start save in CoreData");
saveQueue.async {
DispatchQueue.global(qos: .background).async{
do {
try context.save()
} catch {
print("Failed saving")
}
}
}
The above code didn't solve the problem.
Second: The CoreDataManager was not singleton. I thought that this was the problem, so I changed it to:
class CoreDataHelper {
static let sharedInstance = CoreDataHelper()
private init() {}
static func getInstance() -> CoreDataHelper {
return sharedInstance
}
//...
}
Third: I changed the CoreData Stack setting
static var managedObjectContext: NSManagedObjectContext = {
let coordinator = persistentStoreCoordinator
var managedObjectContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
}()
ConcurrencyType used to be mainQueueConcurrencyType
None of these changes resolved the problem
Crash detail:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber length]: unrecognized selector sent to instance 0xb000000000014153'
*** First throw call stack:
(0x18485cf48 0x19940ff80 0x184863c5c 0x184860c00 0x184764cac 0x18482c978 0x18476de38 0x18460f134 0x1845ebda0 0x1845ed47c 0x18453f2fc 0x184509f04 0x1845d0fdc 0x1845d8fd8 0x1025b5c68 0x1025c181c 0x1845cb830 0x184509ab0 0x18452e1d8 0x1005bce00 0x10029e498 0x100484a08 0x1003c097c 0x1003ca13c 0x1001296e8 0x1025b5ca8 0x1025b5c68 0x1025bb710 0x1848141f8 0x184812060 0x184740ca0 0x18f97c088 0x189e58ffc 0x10011c8e0 0x199c5e8b8)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

import UIKit
import CoreData
class CoreDataHandler: NSObject {
func getContext() -> NSManagedObjectContext{
let appdelegate = UIApplication.shared.delegate as! AppDelegate
return appdelegate.persistentContainer.viewContext
}
func saveDataToCoreData(username:String,password:String) -> Bool{
let entity = NSEntityDescription.entity(forEntityName:"Entity", in: getContext())
let manageObect = NSManagedObject(entity: entity!, insertInto: getContext())
manageObect.setValue(username,forKey:password)
do{
try getContext().save()
return true
}
catch{
return false
}
}
func fetchAllData() -> [Entity]?{
do{
let result:[Entity]? = try getContext().fetch(Entity.fetchRequest())
return result
}
catch{
return nil
}
}
func delete(ManagedObj:Entity) -> Bool{
getContext().delete(ManagedObj)
do{
try getContext().save()
return true
}
catch{
return false
}
}
func cleanMyCoreData() -> Bool{
let delete = NSBatchDeleteRequest(fetchRequest:Entity.fetchRequest())
do{
try getContext().execute(delete)
return true
}
catch{
return false
}
}
func filterByPredicate(pred:NSPredicate) -> [Entity]?{
let fetchReq:NSFetchRequest<Entity> = Entity.fetchRequest()
fetchReq.predicate = pred
do{
let entity = try getContext().fetch(fetchReq)
return entity
}
catch{
return nil
}
}
}