Swift Core Data - arrays not loading properly

Question

Im trying to implement a simple to-do feature to my app with Core Data, but I got stuck on loading the added arrays of items. The to-do has 2 views (category view and a corresponding items view). I implemented NSPredicate to filter our the corresponding items based on category, but it only loads the last added item. When I delete the predicate, it shows every single added item obviously.

Also, when I add a new array, I noticed an error for the previous added item in the Debug area:

error save context Error Domain=NSCocoaErrorDomain Code=1570 "parentCategory is a required value." UserInfo={NSValidationErrorObject=<Echieve.Item: 0x6000019fc410> (entity: Item; id: 0xdb0af4c047f4bf03 <x-coredata://F4D9D28E-242A-4BEE-A528-C067AF1F8909/Item/p89>; data: {
done = 0;
parentCategory = nil;
title = 1111;

So Im not sure whether there is a problem in saving or loading of the Items.

var itemArray = [Item]()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
var selectedCategory: Category? {
    didSet {
        loadItems()
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    loadItems()

}

// MARK: - Table view data source

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    return itemArray.count
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = super.tableView(tableView, cellForRowAt: indexPath)
    let item = itemArray[indexPath.row]
    cell.textLabel?.text = item.title
    cell.accessoryType = item.done ? .checkmark : .none

    return cell
}

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    itemArray[indexPath.row].done = !itemArray[indexPath.row].done
    saveItems()
    tableView.deselectRow(at: indexPath, animated: true)
}

override func updateModel(at index: IndexPath) {
    context.delete(itemArray[index.row])
    itemArray.remove(at: index.row)
    saveItems()
}

@IBAction func addNewItem(_ sender: Any) {
    var alertTextField = UITextField()
    let alert = UIAlertController(title: "Add new Item", message: "", preferredStyle: .alert)
    alert.addTextField { (textField) in
               textField.placeholder = "enter the name"
            alertTextField = textField
           }
    let action =  UIAlertAction(title: "Add new Item", style: .default) { (action) in

        let newItem = Item(context: self.context)
        newItem.title = alertTextField.text!
        newItem.done = false
        newItem.parentCategory = self.selectedCategory
        self.itemArray.append(newItem)
        self.saveItems()

    }
    let cancel = UIAlertAction(title: "Cancel", style: .default) { (action) -> Void in
        print("Cancel button tapped")
    }
    alert.addAction(action)
    alert.addAction(cancel)

    present(alert,animated: true,completion: nil)
    tableView.reloadData()
}

func saveItems() {

    do {
        try context.save()

    } catch {
        print("error save context \(error) ")
    }
    tableView.reloadData()
}


func loadItems(with request: NSFetchRequest<Item> = Item.fetchRequest() , predicate : NSPredicate? = nil)
{
    let categoryPredicate = NSPredicate(format :"parentCategory.name MATCHES %@",selectedCategory!.name!)
    //print(categoryPredicate)
    if let additionalPredicate = predicate
    {
        request.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [categoryPredicate , additionalPredicate])
    }
    else
    {
        request.predicate = categoryPredicate
    }
    print(request.predicate!)
           do{
               itemArray = try context.fetch(request)

           }
           catch
           {
               print("error when fetch result \(error)")
           }
    tableView.reloadData()
}

override func viewWillAppear(_ animated: Bool) {
  super.viewWillAppear(animated)
  loadItems()
}

Thank you very much for anny suggestions.

Your Item object has one to many relationship with Category object in core data model, right? — Vahagn Gevorgyan
– Vahagn Gevorgyan, Commented Jan 23, 2020 at 22:09

trapper · Accepted Answer · 2020-01-24 04:14:52Z

1

Make sure your category -> item relationship is 1-to-many. Probably what is happening now is you have 1-to-1 so each time you set parent category on a new item it unsets the previous one.

Also instead of

let categoryPredicate = NSPredicate(format :"parentCategory.name MATCHES %@",selectedCategory!.name!)

just do

let categoryPredicate = NSPredicate(format :"parentCategory = %@", selectedCategory!)

answered Jan 24, 2020 at 4:14

trapper

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1 Comment

Jaroslav Over a year ago

Thanx a lot, that fixed the problem :)

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