Create/edit in a child context

ChildContext.swift

import UIKit
import CoreData

class Ticket: NSManagedObject { }

class TicketListViewController: UITableViewController {
    var persistentCoordinator: NSPersistentContainer!
    var tickets: [Ticket]!

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let vc = segue.destination as! TicketEditorViewController

        switch segue.identifier! {
        case "createNewTicket":
            vc.parentContext = persistentCoordinator.viewContext

        case "editExistingTicket":
            let indexPath = tableView.indexPathForSelectedRow!
            vc.ticket = tickets[indexPath.row]

        default:
            break
        }
    }
}

final class TicketEditorViewController: UIViewController {
    private let editContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)

    var parentContext: NSManagedObjectContext!
    var ticket: Ticket?

    override func viewDidLoad() {
        super.viewDidLoad()

        if let objectId = ticket?.objectID {
            // We are editing an existing ticket.
            editContext.parent = ticket!.managedObjectContext
            ticket = (editContext.object(with: objectId) as! Ticket)
        } else {
            // We are creating a new ticket.
            editContext.parent = parentContext
            ticket = Ticket(context: editContext)
        }
    }

    override func shouldPerformSegue(withIdentifier identifier: String, sender: Any?) -> Bool {
        view.endEditing(true)

        if identifier == "done" {
            // validate all inputs and return appropriate value
            return true
        }

        return super.shouldPerformSegue(withIdentifier: identifier, sender: sender)
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        guard segue.identifier == "done", editContext.hasChanges else { return }

        try! editContext.save()
        try! editContext.parent!.save()
    }
}