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

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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.

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