快速使用非可选对象将其视为可选

Question

I have a coreData NSManagedObject as follows:

public class Records: NSManagedObject {
    @NSManaged public var uid: String
    @NSManaged public var datetime: Date
}

In addition, I have a helper to retrieve the record by UID:

func getRecordByUid(uid: String) -> Records!{
    do {
        let fetchRequest : NSFetchRequest<Records> = Records.createFetchRequest()
        fetchRequest.predicate = NSPredicate(format: "uid = %@", uid)
        let result: [Records] = try container.viewContext.fetch(fetchRequest)
        return result.first
    } catch {
        print(error.localizedDescription)
        return nil
    }
}

Now, in my view controller I used a core-data object as non-optional (for adding new record or editing existing record purpose) as described below:

class AddRecordViewController: UIViewController {

    var container: NSPersistentContainer!
    var record: Records!
    var currentUid = ""
    @IBOutlet weak var dateTextField: PickerBasedTextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        // initialise core data
        container = NSPersistentContainer(name: "MyModel")
        container.loadPersistentStores { (storeDescription, error) in
            self.container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy

            if let error = error {
                print("Unsolved error \(error.localizedDescription)")
            }
        }

        if let existingRecord = Facade.share.model.getRecordByUid(uid: currentUid) {
            record = existingRecord
        } else {
            record = Records(context: self.container.viewContext)
        }

        // datePicker
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        dateTextField.text = formatter.string(from: record.datetime)

        ...
    }
}

The problem is that it cause an error in dateTextField.text = ... line, because it thinks the record is optional, however it isn't a case:

(lldb) po record
▿ Optional<Records>

Fatal error: Unexpectedly found nil while unwrapping an Optional value

What should I do?

Answer 1

I think that dateTextField is probably nil, and the fatal error is related to it. Either that, or Records(context: self.container.viewContext) is a failable initializer that returns a nil object in some cases.

Answer 2

I think your code would behave much better if you wrapped the fetch with the create into one method that always returns an object.

Something like

func getOrCreateRecord(uid: String) -> Records{
    var record: Records?
    do {
        let fetchRequest : NSFetchRequest<Records> = Records.createFetchRequest()
        fetchRequest.predicate = NSPredicate(format: "uid = %@", uid)
        let result: [Records] = try container.viewContext.fetch(fetchRequest)
        record = result.first
    } catch {
        print(error.localizedDescription)
    }

    return record ?? Records(context: container.viewContext)
}

There still might be an issue with the text field but I still think it makes sense to create a wrapper method for this logic.