lost data in the coreData - swift

Question

My app will show teacher shedule, in the first controller teacher need to choose the right pair (first, second, third) and then write nessesary data (like what the subject name, room, number of group) now in my code if i write data in first pair and save, it will show to me, but if i write data in second pair and choose save button, the previous data in first pair is lost, so i have a problem with losing data, this is code for controller where i choose pair:
class ChoosePair: UIViewController {
enum choosePair: Int{
case FirstPair = 21
case SecondPair = 22
case ThirdPair = 23
case FourPair = 24
}
#IBAction func PairButtons(_ sender: UIButton){
guard let day = choosePair.init(rawValue: sender.tag) else { return }
switch day {
case .FirstPair:
let FirstPair = self
UserDefaults.standard.set(21, forKey: "pairId")
performSegue(withIdentifier: "SheduleTeacher", sender: self)
break
case .SecondPair:
let SecondPair = self
UserDefaults.standard.set(22, forKey: "pairId")
performSegue(withIdentifier: "SheduleTeacher", sender: SecondPair)
break
case .ThirdPair:
let ThirdPair = self
UserDefaults.standard.set(23, forKey: "pairId")
performSegue(withIdentifier: "SheduleTeacher", sender: ThirdPair)
break
case .FourPair:
let FourPair = self
UserDefaults.standard.set(24, forKey: "pairId")
performSegue(withIdentifier: "SheduleTeacher", sender: FourPair)
break
}
}
}
And the code for second controller(where i write data and save it in CoreData)
class SheduleTeacher: UIViewController {
var pairId = UserDefaults.standard.integer(forKey: "pairId")
#IBOutlet weak var subjectLabel: UILabel!
#IBOutlet weak var roomLabel: UILabel!
#IBOutlet weak var timeLabel: UILabel!
#IBOutlet weak var emailLabel: UILabel!
#IBOutlet weak var groupLabel: UILabel!
#IBOutlet weak var captainLabel: UILabel!
#IBOutlet weak var subjectField: UITextField!
#IBOutlet weak var roomField: UITextField!
#IBOutlet weak var timeField: UITextField!
#IBOutlet weak var emailField: UITextField!
#IBOutlet weak var groupField: UITextField!
#IBOutlet weak var captainField: UITextField!
let appDelegate = UIApplication.shared.delegate as! AppDelegate
override func viewDidLoad() {
super.viewDidLoad()
let context = appDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")
request.returnsObjectsAsFaults = false
do {
let result = try context.fetch(request)
for data in result as! [NSManagedObject] {
subjectField.text = data.value(forKey: "subject\(pairId)") as? String
roomField.text = data.value(forKey: "room\(pairId)") as? String
timeField.text = data.value(forKey: "time\(pairId)") as? String
emailField.text = data.value(forKey: "emailGroup\(pairId)") as? String
groupField.text = data.value(forKey: "group\(pairId)") as? String
captainField.text = data.value(forKey: "captain\(pairId)") as? String
}
} catch {
print("Failed")
}
subjectLabel.layer.borderWidth = 1.0
roomLabel.layer.borderWidth = 1.0
timeLabel.layer.borderWidth = 1.0
emailLabel.layer.borderWidth = 1.0
groupLabel.layer.borderWidth = 1.0
captainLabel.layer.borderWidth = 1.0
}
#IBAction func saveButton(_ sender: UIButton) {
let context = appDelegate.persistentContainer.viewContext
let entity = NSEntityDescription.entity(forEntityName: "Users", in: context)
let newUser = NSManagedObject(entity: entity!, insertInto: context)
newUser.setValue(self.subjectField!.text, forKey: "subject\(pairId)")
newUser.setValue(self.roomField!.text, forKey: "room\(pairId)")
newUser.setValue(self.timeField!.text, forKey: "time\(pairId)")
newUser.setValue(self.emailField!.text, forKey: "emailGroup\(pairId)")
newUser.setValue(self.groupField!.text, forKey: "group\(pairId)")
newUser.setValue(self.captainField!.text, forKey: "captain\(pairId)")
do {
try context.save()
} catch {
print("Failed saving")
}
}
}
And photo what I now have in CoreData
photo

Answer 1

Predicates are used to limit the fetch to only get certain entities.
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")
request.returnsObjectsAsFaults = false
Does not set a predicate so it always returns all the Users entities there are. The following has you iterate over every entity, that's why there is a for-loop.
for data in result as! [NSManagedObject] {
Here is an example how you can use a predicate to only get entities with entity.pairId == pairId.
override func viewDidLoad() {
super.viewDidLoad()
let context = AppDelegate.shared.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Users")
request.returnsObjectsAsFaults = false
request.predicate = NSPredicate(format: "pairId = %#", argumentArray: [pairId])
do {
let results = try context.fetch(request)
guard results.count == 1 else {
fatalError("Bad count: \(results.count)")
}
guard let data = results.first! as? NSManagedObject else {
fatalError("No NSManagedObject")
}
context.performAndWait {
subjectField.text = data.value(forKey: "subject\(pairId)") as? String
roomField.text = data.value(forKey: "room\(pairId)") as? String
timeField.text = data.value(forKey: "time\(pairId)") as? String
emailField.text = data.value(forKey: "emailGroup\(pairId)") as? String
groupField.text = data.value(forKey: "group\(pairId)") as? String
captainField.text = data.value(forKey: "captain\(pairId)") as? String
}
} catch {
print("Failed")
}
// ...
}
The entity must of course have said attribute pairId for the predicate to work.
You would do something like this in the save() method too. There you could update the retrieved Users entity/create a new one if one does not exist.
One alternative is to delete the old one if one so exists and always create a new one on save.
The other alternative to "create a new one if one does not exist" is to pre-create for all four buttons and then fetch the entities on save and update them there. You would however have to check on startup too if they exist already else you would create on every startup four.

Answer 2

In your saveButton func you create a new Users instance every time which mean data from pair two will not be written together with data for pair one but as a separate record. You need to update the existing object, the one you fetched in viewDidLoad, instead. (I very much doubt any data is lost)
That being said I think you need to rethink your design, having duplicate (or more) fields in the same entity looks like an awkward design that will be hard to maintain. A better solution would be to only have one group attribute, one subject attribute and so on and complement it with an attribute that holds the pairId.
Also, why is the entity name Users, it seems to hold no kind of user id?