Turning objects filtered from managedObjectContext into an NSArray

Question

I'm relatively new to iOS and I find myself "thrown to the wolves" on a Core Data assignment. I'm trying to create an array of Note objects using a NSPredicate to search a managedObjectContext. It's not working, but I think I'm close to the "finish line". Here's what I've got:

I have a managedObjectContext instantiated and there are Note objects in it.

I have a variable I created called filteredNotes at the top of the class that's instantiated empty (at least I think so).

var filteredNotes: [Note] = []

Further down, I have a function that I want to "fill up" the filteredNote array with note objects that match a predicate. Here's how I'm trying to do it:

    let resultPredicate = NSPredicate(format: "noteTitle contains[c] %@", searchBar.text)

    filteredNotes = (managedObjectContext as! NSArray).filteredArrayUsingPredicate(resultPredicate)

The compiler has this to say about it:

1. Cast from 'NSManagedObjectContext?' to unrelated type 'NSArray' always fails
2. Cannot assign a value of type '[AnyObject]' to a value of type '[Note]'

I see a lot of examples of vanilla NSArrays (not managedObjectContexts) doing this and I'm stumped why I can't do it w/ a managedObjectContext that's filled with Note objects.

Here's what my Note: NSManagedObject looks like:

import Foundation
import CoreData

class Note: NSManagedObject {

    @NSManaged var dateCreated: NSDate
    @NSManaged var dateEdited: NSDate
    @NSManaged var noteTitle: String
    @NSManaged var noteBody: String

}

Any suggestions on how to create the filteredNote array?

Answer 1

The managed object context has nothing to do with an array. It cannot be "filled" with objects. It is simply an abstract class that gives you access to your data.

The way you get objects from your Core Data store is as follows: make a fetch request, optionally add filter and/or sorting to the request, fetch the objects.

let request = NSFetchRequest(entityName:"Note")
let result = managedObjectContext.executeFetchRequest(request error:nil) as [Note]

You can now either filter this array (with filteredArrayUsingPredicate after casting to NSArray) or you can add your predicate to the original fetch request (which should even be more efficient).