How do you update a CoreData entry that has already been saved in Swift?

Question

I'm not sure what I'm doing wrong here, but when I save the first time into coredata, it works just fine. When I try to overwrite that, it doesn't.

func testStuff() {     var token = loadLoginData()     println("Token \(token)")     saveLoginData("New Token")     var newToken = loadLoginData()     println("Token \(newToken)") }  func saveLoginData(accessToken: String) {     var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)     var context: NSManagedObjectContext = appDel.managedObjectContext!     // save data to core data     var loginData = NSEntityDescription.insertNewObjectForEntityForName("LoginData", inManagedObjectContext: context) as NSManagedObject     loginData.setValue(accessToken, forKey: "accessToken")     context.save(nil)     println("Done saving user") }  /* Output Token Optional("12345") Done saving user Token Optional("12345") */ 

Load Login Data Func the function that calls on saveLogin data

func loadLoginData() -> String? {     var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)     var context: NSManagedObjectContext = appDel.managedObjectContext!      var request = NSFetchRequest(entityName: "LoginData")     request.returnsObjectsAsFaults = false      var results: NSArray = context.executeFetchRequest(request, error: nil)!     if (results.count > 0) {         var userData: NSManagedObject = results[0] as NSManagedObject         var accessToken: String = userData.valueForKey("accessToken") as String          return accessToken.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())      } else {         println("0 results returned, potential error")         return nil     } } 

Answer 1

Since batchupdate is more useful in larger chunks of data, I think this is a more subtle approach.

func saveLoginData(accessToken: String, userName: String) {     var appDel: AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)     var context: NSManagedObjectContext = appDel.managedObjectContext!      var fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "LoginData")     fetchRequest.predicate = NSPredicate(format: "userName = %@", userName)      if let fetchResults = appDel.managedObjectContext!.executeFetchRequest(fetchRequest, error: nil) as? [NSManagedObject] {         if fetchResults.count != 0{              var managedObject = fetchResults[0]             managedObject.setValue(accessToken, forKey: "accessToken")              context.save(nil)         }     } } 

I tried to translate it a bit to your situation if I'm not mistaken, but have not tested it.

fetchRequest.predicate basically sets the filter on the attribute userName from the entity LoginData, with the (user)name you enter when calling the function. Assuming in this example you have only one username with the same name. Then it does a fetchrequest with the given filter, so you can change it's value with setValue with the accesToken you also enter when calling the function. The code after: if fetchResults.count != 0 , only executes when the username exists.

Answer 2

Updated for Swift 4 & XCode 9.2

To answer your question...

How do you update a CoreData entry that has already been saved in Swift?

You first need to get a reference to your AppDelegate and viewContext. You then need to set up a NSFetchRequest for the Entity you are looking to update, in my example that would be "Alert". You then set up your fetch to find the result you are looking for. In the example, my result found Alerts by their creation date and alert type.

To further read how to query using a predicate. Stack Overflow Example & Apple Documentation

I then context.fetch(fetchRequest), set the results to the value I wanted to update, and dealt with errors in a try catch. Finally I context.save().

let appDelegate = UIApplication.shared.delegate as! AppDelegate let context = appDelegate.persistentContainer.viewContext let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Alert")  fetchRequest.predicate = NSPredicate(format: "creationDate = %@ AND alertType = %&",                                          argumentArray: [creationDate, alertType])  do {     let results = try context.fetch(fetchRequest) as? [NSManagedObject]     if results?.count != 0 { // Atleast one was returned          // In my case, I only updated the first item in results         results[0].setValue(yourValueToBeSet, forKey: "yourCoreDataAttribute")     } } catch {     print("Fetch Failed: \(error)") }  do {      try context.save()     } catch {     print("Saving Core Data Failed: \(error)") }