Hello,I'm learning CoreData but my Tutorial is about one year old so not everything is up to date and I don't understand where the problem is. My Project includes an TableViewController with an bar button item. Here is the codeCoreDataResource.swift:import UIKit import CoreData class CoreDataResource { // /Document var documentDir : URL { let allUrls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask) return allUrls[0] } let appDelegate = UIApplication.shared.delegate as! AppDelegate private var managedObjectModel: NSManagedObjectModel { guard let url = Bundle.main.url(forResource: "Listen", withExtension: "momd") else { fatalError("fix me: not found?") } guard let model = NSManagedObjectModel(contentsOf: url) else { fatalError("error in the model?") } return model } private var storeCoordinator: NSPersistentStoreCoordinator { let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel) let url = self.documentDir.appendingPathComponent("Listen.sqlite") do { try coordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: url, options: nil) } catch { print(error) } return coordinator } var managedContext: NSManagedObjectContext { let context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType) context.persistentStoreCoordinator = self.storeCoordinator return context } func saveContext() { if managedContext.hasChanges { do { try managedContext.save() } catch { print(error) } } } func loadLists() -> [Liste] { let request: NSFetchRequest = Liste.fetchRequest() var listen = [Liste]() do{ listen = try managedContext.fetch(request) } catch { print(error) } return listen } func newList(_ name: String) { let newList = NSEntityDescription.insertNewObject(forEntityName: "Liste", into: managedContext) as! Liste newList.name = name saveContext() } }ListTableViewController.swift:import UIKit class ListTableViewController: UITableViewController { let appDelegate = UIApplication.shared.delegate as! AppDelegate var listen = [Liste]() override func viewDidLoad() { super.viewDidLoad() reloadList() } private func reloadList() { listen = appDelegate.coreDataResource.loadLists() } @IBAction func addDummyData(_ sender: Any) { appDelegate.coreDataResource.newList("Test entry") appDelegate.coreDataResource.saveContext() reloadList() } // MARK: - Table view data source override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell { let cell = tableView.dequeueReusableCell(withIdentifier: "listCell", for: indexPath) let liste = listen[indexPath.row] cell.textLabel?.text = liste.name return cell } override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int { // #warning Incomplete implementation, return the number of rows return listen.count } }If I press in Simulator on the addDummyData button the following error occurs:CoreData: error: Mutating a managed object 0x6000026b25c0 <x-coredata:///Liste/t8A4529E8-BD3B-4157-B3AF-E8B011B6C46E2> (0x6000005b6300) after it has been removed from its context.I can't find the mistake. Please help me it's frustrating 😀