CoreData with tableView Sections

Question

I have CoreData Model:

And I try use fetchResultsController to display sections and rows. Sections should be from Category entity and rows should be from Items entity. How I can achieve this?

I use code:

override func numberOfSections(in tableView: UITableView) -> Int {
    return fetchResultsController?.sections?.count ?? 1
    }

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    let sectionInfo = fetchResultsController.sections![section]
    return sectionInfo.numberOfObjects
}

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! ItemsTableViewCell


    if let person = fetchResultsController?.object(at: indexPath)  {
        cell.textLabel?.text = person.name
    }


    return cell
}

But with this code I get only Category names. But I want to show Items related to special category. What I should change in

if let person = fetchResultsController?.object(at: indexPath)  {
    cell.textLabel?.text = person.name
}

to display Items for special Category?

My code for configuring fetchResultsController:

func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
  tableView.beginUpdates()
}

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {

  switch type {
  case .insert: guard let indexPath = newIndexPath else { break }
  tableView.insertRows(at: [indexPath], with: .fade)
  case .delete: guard let indexPath = indexPath else { break }
    tableView.deleteRows(at: [indexPath], with: .fade)
  case .update: guard let indexPath = indexPath else { break }
    tableView.reloadRows(at: [indexPath], with: .fade)
  default:
    tableView.reloadData()
  }
    categories = controller.fetchedObjects as! [Category]
}

func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
  tableView.endUpdates()
}

And:

var fetchResultsController: NSFetchedResultsController<Category>!
    let request: NSFetchRequest<Category> = Category.fetchRequest()
    request.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
    fetchResultsController = NSFetchedResultsController<Category>(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    try? fetchResultsController?.performFetch()
    fetchResultsController?.delegate = self
    tableView.reloadData()

Answer 1

You need to base the frc on the Item entity, and use the sectionNameKeyPath to reference the Category name:

var fetchResultsController: NSFetchedResultsController<Item>!
    let request: NSFetchRequest<Item> = Item.fetchRequest()
    request.sortDescriptors = [NSSortDescriptor(key: "list.name", ascending: true)]
    fetchResultsController = NSFetchedResultsController<Item>(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: “list.name”, cacheName: nil)
    try? fetchResultsController?.performFetch()
    fetchResultsController?.delegate = self
    tableView.reloadData()