Update CoreData Object - ios

Question

I'd like to update a CoreData Object.
Backgrund: I made an app which includes a UITableView. In the textLabel of the UITableViewCell is a name. In the detailTextLabel of this cell is a date which can be changed/updated. Now I'd like to change this date.
I wrote the following code:
var people = [NSManagedObject]()
func saveDate(date: NSDate) {
//1
let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let managedContext = appDelegate.managedObjectContext!
//2
let entity = NSEntityDescription.entityForName("Person", inManagedObjectContext:managedContext)
let person = people[dateIndexPath.row]
//3
person.setValue(date, forKey: "datum")
//4
var error: NSError?
if !managedContext.save(&error) {
println("Could not save \(error), \(error?.userInfo)")
}
//5
people.append(person)
tableView.reloadData()
}
Now, if I run this code:
The date is successfully updated but the cell in which the date has been updated is displayed 2 times. For example if I added 3 cells and changed the date in the 3rd cell, I now get 4 cells displayed and 2 of them have the same content/are duplicated.
Does someone knows how to solve this problem?

Answer 1

You're adding an additional object to your array each time. Your updated Person is already in the array and will display the new information when you reload your table data. To fix this, just take out this line:
people.append(person)

Answer 2

You're going to want to associate some kind of unique identifier attribute to your Person class. This allows to retrieve that same object later using it identifier. I would suggest using a UUID string value, called personID, identifier, or something similar.
You can override the awakeFromInsert method on your Person class like so:
// This is called when a new Person is inserted into a context
override func awakeFromInsert()
{
super.awakeFromInsert()
// Automatically assign a randomly-generated UUID
self.identifier = NSUUID().UUIDString
}
When you want to edit an existing Person, you want to retrieve it by the UUID. I suggest a class function like so (in the Person class):
class func personWithIdentifier(identifier: String, inContext context: NSManagedObjectContext) -> Person?
{
let fetchRequest = NSFetchRequest(entityName: "Person")
fetchRequest.predicate = NSPredicate(format: "identifier ==[c] %#", identifier)
fetchRequest.fetchLimit = 1 // Only want the first result
var error : NSError?
let results = context.executeFetchRequest(fetchRequest, error: &error) as [Person]
// Handle error here
return results.first?
}
This way you can use the following function:
let identifier = ...
let context = ...
var person = Person.personWithIdentifier(identifier, inContext: context)
if let person = person
{
// Edit the person
person.value = // change the values as you need
}
else
{
// Person does not exist!
person = // possibly create a person?
}