Updating CoreData Entity or saving a new one - ios

Question

I'm fairly new to CoreData, and I'm trying to make a game. I have a couple of questions I was hoping you guys could help me out with some guidance:
- does GameKit already have some sort of CoreData integrated in it? I am not sure if I am overthinking this CoreData stuff if there's already something that replaces it in GameKit.
. . .
Anyways, assuming the answer to the above question is "no. GameKit has nothing to save your game". I will proceed with my current "Save game" code which is the following:
func saveCurrentMatch()
{
/* CORE DATA STUFF:
FIRST NEED TO VERIFY IF THIS GAME HAS BEEN PREVIOUSLY SAVED, IF SO THEN UPDATE, ELSE JUST SAVE
Entity: MatchData
Attributes: scoreArray (String), playerArray (String), myScore (Int), matchID (Int), isWaiting (Bool), isRealTime (Bool), gameLog (String)
*/
let context = myAppDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
request.returnsObjectsAsFaults = false
do
{
let gamesInProgress = try context.fetch(request)
print (gamesInProgress.count)
if gamesInProgress.count > 0 //HERE CHANGE THIS TO LOOK FOR THE MATCH ID OF THIS GAME!!
{
gameExistsinCD = true
}
else
{
gameExistsinCD = false
}
}
catch
{
print ("Error Reading Data: \(error.localizedDescription)")
}
if gameExistsinCD
{
//CODE TO UPDATE MATCH INSTEAD OF SAVING NEW ONE
}
else
{
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)
matchData.setValue(isRealTime, forKey: "isRealTime")
matchData.setValue(currentScore?[0], forKey: "myScore")
matchData.setValue(currentScore?.map{String($0)}.joined(separator: "\t"), forKey: "scoreArray") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
matchData.setValue(currentPlayers?.joined(separator: "\t"), forKey: "playerArray")
matchData.setValue(true, forKey: "isWaiting") //will change later to update accordingly.
matchData.setValue(matchID, forKey: "matchID")
matchData.setValue(gameLog, forKey: "gameLog")
do
{
try context.save()
print ("CoreData: Game Saved!")
}
catch
{
print ("Error Saving Data: \(error.localizedDescription)")
}
}
}
My main concern is on the fetch request, how do I check all the core-data if this match has already been saved? and if so, whats the code for updating an Entity instead of inserting a new one?
Any guidance is appreciated, thanks!

Answer 1

Don't let Core Data scare you. It can be a fine way to save local data and despite some comments, it is not slow when done right. In fact, Core Data can be quite fast.
You can simplify your code a lot by using your Object class in a more normal fashion instead of using setValue calls. Your create code can be changed to this:
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
if let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context) as? MatchData {
matchData.isRealTime = isRealTime
matchData.myScore = currentScore?[0]
matchData.scoreArray = currentScore?.map{String($0)}.joined(separator: "\t") // IS THIS CODE CORRECT? I'M TRYING TO SAVE AN ARRAY OF INTS INTO A SINGLE STRING
// You can certainly save it this way and code it in and out. A better alternative is to have a child relationship to another managed object class that has the scores.
matchData.playerArray = currentPlayers?.joined(separator: "\t")
matchData.isWaiting = true
matchData.matchID = matchID
matchData.gameLog = gameLog
}
This is a much more readable and normal way to set your object properties. Any time you change a property on a core data managed object then it will get saved the next time you save the context.
As far as finding a current record that matches the ID, I like to add classes like that to my Managed Object class itself:
class func findByID(_ matchID: String) -> MatchData? {
let myAppDelegate = UIApplication.shared.delegate as! AppDelegate
let context = myAppDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "MatchData")
let idPredicate = NSPredicate(format: "matchID = \(matchID)", argumentArray: nil)
request.predicate = idPredicate
var result: [AnyObject]?
var matchData: MatchData? = nil
do {
result = try context.fetch(request)
} catch let error as NSError {
NSLog("Error getting match: \(error)")
result = nil
}
if result != nil {
for resultItem : AnyObject in result! {
matchData = resultItem as? MatchData
}
}
return matchData
}
Then any place you need the match data by ID you can call the class function:
if let matchData = MatchData.findByID("SomeMatchID") {
// Match exists
}

Answer 2

Core data is basically wrapper around SQL database. It is very efficient when you are working with high volume of data that need to be stored. So please consider either you had such requirements, otherwise perhaps it can be wise to store data in user defaults, or settings.
If it is, there is few things you need to know.
It is very useful to create you own model classes. Open core data model file, open "Editor/Create NSManagedObject subclass". It will allow you to refer direct properties, instead of KVC(setValue:forKey:).
Alway mind what thread you are working in. It is unsafe to work with objects, created in other threads.
Your gamesInProgress contains array of objects you fetched from your database.
So basically instead of
if gameExistsinCD
{
//CODE TO UPDATE MATCH INSTEAD OF SAVING NEW ONE
}
else
{
// CODE TO SAVE A NEW MATCH FOR THE FIRST TIME
let matchData = NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)
matchData.setValue(isRealTime, forKey: "isRealTime")
<...>
you can do
let matchData = (gamesInProgress.first ??
NSEntityDescription.insertNewObject(forEntityName: "MatchData", into: context)) as! <YouEntityClass>
matchData.isRealTime = isRealTime
<...>
PS: https://www.raywenderlich.com/173972/getting-started-with-core-data-tutorial-2