How do you fetch NSSet from NSManagedObject in Swift? - ios

Question

I have a one to many relationship from Set to Card for a basic Flashcard App modelled in my Core Data.
Each Set has a set name, set description, and a relationships many card1s. Each Card1 has a front, back, and photo. In my table view, I've managed to retrieve all saved Sets from core data and display them. Now I want to fetch each Set's cards when a user clicks on the appropriate cell in my next view controller.
This is my code for the table view controller:
// MARK: Properties
var finalArray = [NSManagedObject]()
override func viewDidLoad() {
getAllSets()
println(finalArray.count)
}
func getAllSets() {
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext!
let fetchRequest = NSFetchRequest(entityName:"Set")
var error: NSError?
let fetchedResults = managedContext.executeFetchRequest(fetchRequest,error: &error) as? [NSManagedObject]
println("Am in the getCardSets()")
if let results = fetchedResults {
finalArray = results
println(finalArray.count)
}
else {
println("Could not fetch \(error), \(error!.userInfo)")
}
}
// MARK: Displaying the data
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return 1
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return finalArray.count
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as! SetTableViewCell
let sets = finalArray[indexPath.row]
cell.setName.text = sets.valueForKey("setName")as? String
cell.setDescription.text = sets.valueForKey("setDescription")as? String
return cell
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "ShowDetail" {
let dest = segue.destinationViewController as! Display
// Get the cell that generated this segue.
if let selectedCell = sender as? SetTableViewCell {
let indexPath = tableView.indexPathForCell(selectedCell)!
let selectedSet = finalArray[indexPath.row]
dest.recievedSet = selectedSet
}
}
}
In my destination view controller, how would I go about retrieving all the cards in that the recievedSet? I've tried converting the NSSet to an array and casting it to a [Card1] array but when I attempt to display the first Card1's front String property onto the label, the app crashes, giving me the error
CoreData: error: Failed to call designated initializer on NSManagedObject class 'NSManagedObject'
fatal error: Array index out of range
This is my code for the detailed viewController.
#IBOutlet weak var front: UILabel!
var finalArray = [Card1]()
finalArray = retrievedSet.allObjects as![Card1]
front.text = finalArray[0].front

Answer 1

Give your detail controller a property of type CardSet (I use "CardSet" because "Set" is a Swift built-in type name). You pass the selected set to this controller.
You could have a property by which you sort, or generate an array without a particular order with allObjects.
var cardArray = [Card1]()
var cardSet: CardSet?
viewDidLoad() {
super.viewDidLoad()
if let validSet = cardSet {
cardArray = validSet.cards.allObjects as! [Card1]
}
}
Your code is not working because finalArray is of type [CardSet], so finalArray[indexPath.row] is of type CardSet which is not transformable into type NSSet. Rather the relationship to Card1s is the NSSet you are looking for.
Finally, I recommend to give the detail controller a NSFetchedResultsController, have an attribute to sort by and use the passed CardSet in the fetched results controller's predicate.