Primary key can't be changed after an object is inserted - swift

Question

I'm very new to programming.
I am trying to update an object in my Realm database but I get always an error.
I have tried to find the issue but I can't find anyone with a similar issue.
What I'm trying to do is:
I have a Game-Score-App.
It should display the names on Tab1 and on the Tab2 I want to give the user the ability, to change the names of the players. As soon as the ViewDidDisappear I want to write the changes to Realm.
I already figured out how to update the names in the database. And it works properly the first time.
But as soon as I go a second time on the Tab2 and go back to Tab1 again, I get the message "Primary key can't be changed after an object is inserted."
Any Ideas?
class Games: Object {
#objc dynamic var game_id = UUID().uuidString
#objc dynamic var gameName: String = ""
var playerNames = List<String>()
override class func primaryKey() -> String? {
return "game_id"
}
}
class FirstPageVC: UIViewController {
#IBOutlet var playerNameLabels: [UILabel]!
#IBOutlet weak var gameNameLabel: UILabel!
let realm = try! Realm()
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
let games = realm.objects(Games.self)
gameNameLabel.text = games[0].gameName
for i in 0...playerNameLabels.count - 1 {
playerNameLabels[i].text = games[0].playerNames[i]
}
}
}
class SecondPageVC: UIViewController {
#IBOutlet var playerNameTextbox: [UITextField]!
#IBOutlet weak var gameNameTextbox: UITextField!
#IBOutlet weak var numberOfIndex: UITextField!
let realm = try! Realm()
var playerNames: [String] = []
var gameName: String = ""
var game = Games()
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(true)
if realm.objects(Games.self).count != 0 {
let games = realm.objects(Games.self)
gameNameTextbox.text = games[0].gameName
for i in 0...playerNameTextbox.count - 1 {
playerNameTextbox[i].text = games[0].playerNames[i]
}
}
}
#IBAction func addButton(_ sender: UIButton) {
gameName = gameNameTextbox.text!
for i in 0...playerNameTextbox.count - 1 {
playerNames.append(playerNameTextbox[i].text!)
}
let items = realm.objects(Games.self)
let number = Int(numberOfIndex.text!)
game.game_id = items[number!].game_id
game.gameName = gameName
game.playerNames.append(objectsIn: playerNames)
try! realm.write {
realm.add(game, update: .modified)
}
}
}

Answer 1

The problem is your Realm object structure. Anything that could possibly ever be changed should not be used as a primary key.
Also note from the Realm Documentation
Once an object with a primary key is added to a Realm, the primary key
cannot be changed.
To expand on that, it's often best practice to disassociate an objects key (e.g. primary key) from the rest of the properties of an object.
Here's how to do that
class Games: Object{
#objc dynamic var game_id = UUID().uuidString
#objc dynamic var gameName: String = ""
var playerNames = List<String>()
override class func primaryKey() -> String? {
return "game_id"
}
}
UUID().uuidString will generate a unique string for every object that's created and will look something like this string
CDEA69EA-AC84-4465-ABE3-DDA29D31B925
Once the object is created, you can use it to load that specific object or update it's properties.
See Objects with Primary Keys
Here's how to change the game name
let item = realm.object(ofType: Game.self, forPrimaryKey: "CDEA69EA-AC84-4465-ABE3-DDA29D31B925")!
try! realm.write {
game.gameName = "Pwn You!"
}

Answer 2

Try this solution:
Replace the code in viewDidDisappear after the end of for loop with the following code:
if let gameInRealm = realm.objects(Game.self).first{
try! realm.write {
gameInRealm.gameName = gameName
gameInRealm.playerNames = playerNames
}
}else{
game.gameName = gameName
game.playerNames.append(objectsIn: playerNames)
realm.add(game)
}
Explanation (if needed):
The code changes the existing Game properties in case a Game object exists. Otherwise, it creates a new one with the new properties.
Therefore, the else statement should get executed the first time you leave SecondPageVC, and then the if statement will get triggered every other time you leave SecondPageVC.