Querying Core data with predicates - ios

Question

So i am building this app using CoreData.
The two entities I have are Lists and Items. They have a to many relationship i.e. A List can have multiple items.
For example: List1 has Items: item1, item2
I have written the code for storing the Items in the specific list but i am having a difficult time on figuring out how to fetch and proccess the Items from a specific List.
What I have done so far is as follows
func getItemsOnList(){
let app = UIApplication.shared.delegate as! AppDelegate
let context = app.persistentContainer.viewContext
//fetchRequest to get the List
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "List")
let predicate = NSPredicate(format: "title == %#", listName)
fetchRequest.returnsObjectsAsFaults = false
fetchRequest.predicate = predicate
if let fetchResults = try? context.fetch(fetchRequest){
if fetchResults.count > 0 {
for listEntity in fetchResults {
let list = listEntity as! List
print(list.title as Any)
itemsOnList = list.contains!
print(itemsOnList)
print("The list with name:\(list.title)has \(itemsOnList.count) items")
}
}
}
}
This function returns an NSSet which is suppose to contain all the Items in that particular List.
My Data model is :
My questions are:
A. Is the way I coded the getItemsOnList() function correct? Or is there something I am doing wrong.
B. Given that the code is correct and the NSSet I get is correct with all the Items, how would I get each Item in that NSSet in order for me to put it on a TableView.

Answer 1

func getItemsWithFilter(filterQuery:NSPredicate,sortBy:String?,order:Bool) -> Array<Items> {
var fetchedResults:Array<Items> = Array<Items>()
let fetchRequest = NSFetchRequest(entityName: "Items")
fetchRequest.predicate = filterQuery
if sortBy != nil{
let sortDescriptor = NSSortDescriptor(key:sortBy! ,
ascending:order )
let sortDescriptors = [sortDescriptor]
fetchRequest.sortDescriptors = sortDescriptors
}
//Execute Fetch request you can go with your approach to
do {
fetchedResults = try self.mainContextInstance.executeFetchRequest(fetchRequest) as! [Items]
} catch let fetchError as NSError {
print("retrieveById error: \(fetchError.localizedDescription)")
fetchedResults = Array<Items>()
}catch {
fetchedResults = Array<Items>()
}
return fetchedResults
}
for calling this method you can pass the List item in predicate to as query saying fetch Items in which List.id == XXX
let predicate = NSPredicate(format: "ANY list.name in %#", name)
let myResult = self.getItemsWithFilter(predicate,sortBy:nil,order:false)

Answer 2

Answers:
A) Yes. You are using the graph of objects from a fetch. That is the main functionality of Core Data.
B) To fill a table view you cannot use a set. You need some kind of sorted list of elements. That is, an array. Use -orderedArrayUsingDescriptors: to get the sorted array.