How to overwrite Core Data attribute in Swift

Question

I'm trying to update an attribute in Core Data and then display it. However, when I tell the program to display it, it displays the original value.

Based off the code below, username is set to a String. I know 100% that username is saved into Core Data. However, when I try to update it, it saves to Core Data, but prints out the old value. How can I print out only the "newest" value?

import UIKit
import CoreData

class NameSettings: UIViewController {

@IBOutlet var nameText: UITextField!

var userID: String!
var username: String!

override func viewDidLoad() {
    super.viewDidLoad()

    var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)

    var context:NSManagedObjectContext = appDel.managedObjectContext!

    var request = NSFetchRequest(entityName: "Users")

    request.returnsObjectsAsFaults = false

    var results: NSArray = context.executeFetchRequest(request, error: nil)!

    var res = results [0] as NSManagedObject

    userID = res.valueForKey("userID") as String
    username = res.valueForKey("username") as String

    println(username)

    nameText.text = username

}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

@IBAction func saveTapped(sender: AnyObject) {

    //println(userID)

    var query = PFQuery(className:"_User")
    query.getObjectInBackgroundWithId(userID) {
        (update1: PFObject!, error: NSError!) -> Void in
        if error == nil {

            update1["username"] = self.nameText.text
            update1.saveEventually()

            var appDel:AppDelegate = (UIApplication.sharedApplication().delegate as AppDelegate)

            var context:NSManagedObjectContext = appDel.managedObjectContext!

            var updateUser = NSEntityDescription.insertNewObjectForEntityForName("Users", inManagedObjectContext: context) as NSManagedObject

            updateUser.setValue(self.nameText.text, forKey: "username")

            context.save(nil)

            //println(self.nameText.text)

            self.navigationController?.popToRootViewControllerAnimated(true)


        }
    }

}

}

NOTE: All the println's are just for debugging.

With `insertNewObjectForEntityForName` you're inserting a new value. Not overwriting the old. — Lyndsey Scott, Dec 22 '14 at 18:17
Oh....I don't know the in's and out's of Core Data. Would you mind helping me out with fixing this issue? :) — dom999999, Dec 22 '14 at 18:18
Perhaps this answer will help: http://stackoverflow.com/a/10572134/2274694 — Lyndsey Scott, Dec 22 '14 at 18:26
Is there a way that I can delete the current value, and then "insert" the new value? — dom999999, Dec 22 '14 at 18:28
Which core data object are you trying to overwrite? "res" (i.e. the first object)? — Lyndsey Scott, Dec 22 '14 at 18:30
I want to overrite "username". In my core data model, I have an entity named "Users" and an attribute named "username". This is what I want to change. — dom999999, Dec 22 '14 at 18:31
Yeah, but you can have multiple NSManagedObjects in your data model. From your viewDidLoad though, it looks like you're accessing the very first NSManagedObject object: `var res = results [0] as NSManagedObject` — Lyndsey Scott, Dec 22 '14 at 18:33
Ok....so I guess I want to overwrite res. But isn't that going to screw up "UserID"? — dom999999, Dec 22 '14 at 18:33

score 3 · Accepted Answer · answered Dec 22 '14 at 18:43

As your code stands now, you're not overwriting any NSManagedObject; you're inserting a new one, i.e. insertNewObjectForEntityForName.

Instead, what you can do is declare the NSManagedObject you want to save and the NSManagedObjectContext you want to save to as global variables; then simply set a new value for the NSManagedObject's relevant key before saving to the NSManagedObjectContext, ex:

var userID: String!
var username: String!
var res : NSManagedObject!
var context : NSManagedObjectContext!

override func viewDidLoad() {
    super.viewDidLoad()

    //...

    context = appDel.managedObjectContext! // <-- Use global var

    var request = NSFetchRequest(entityName: "Users")

    request.returnsObjectsAsFaults = false

    var results: NSArray = context.executeFetchRequest(request, error: nil)!

    res = results [0] as NSManagedObject // <-- Use global var

    //...
}

@IBAction func saveTapped(sender: AnyObject) {

    //println(userID)

    var query = PFQuery(className:"_User")
    query.getObjectInBackgroundWithId(userID) {
        (update1: PFObject!, error: NSError!) -> Void in

        if error == nil {

            update1["username"] = self.nameText.text
            update1.saveEventually()

            res.setValue(self.nameText.text, forKey: "username")

            context.save(nil)

            //println(self.nameText.text)

            self.navigationController?.popToRootViewControllerAnimated(true)

        }
    }
}

Beautiful! Works perfectly. Thanks for your time and help! At least now I understand where I was going wrong! :) — dom999999, Dec 22 '14 at 18:51

How to overwrite Core Data attribute in Swift

1 Answers1