Core Data NSFetchedResultsController - Total number of records returned

Question

I'm using an NSFetchedResultsController in an iPhone app, and am wondering if there is some easy way of getting the total number of rows returned in all sections.

Instead of getting the [[fetchedResultsController sections] count] and then looping through each section to get its count, can it be done in one line?

Thanks!

Solution 1

This line returns the total number of fetched objects:

[fetchedResultsController.fetchedObjects count]

Solution 2

How about this one?

[fetchedResultsController.sections.valueForKeyPath: @"@sum.numberOfObjects"];

This won't touch the fetched objects at all so it's guaranteed not to fault those.

Solution 3

Swift.

fetchedResultsController.fetchedObjects?.count

Solution 4

Swift 4:

Max Desiatov's suggestion as a Swift extension:

import Foundation
import CoreData

extension NSFetchedResultsController {

    @objc var fetchedObjectsCount: Int {
        // Avoid actually fetching the objects. Just count them. Why is there no API like this on NSFetchResultsController?
        let count = sections?.reduce(0, { (sum, sectionInfo) -> Int in
            return sum + sectionInfo.numberOfObjects
        }) ?? 0
        return count
    }
}

Usage:

let objectCount = fetchedResultsController.fetchedObjectCount

---

Or do it as an inline routine:

// Avoid actually fetching objects. Just count them.
let objectCount = fetchedResultsController.sections?.reduce(0, { $0 + $1.numberOfObjects }) ?? 0

---

Note: The @objc is needed to avoid this compile error:

Extension of a generic Objective-C class cannot access the class's generic parameters at runtime

(See How to write an extension for NSFetchedResultsController in Swift 4)

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Comments

[Neal L]

Thanks! I knew it had to be something simple like that!

[Senseful]

For anyone wondering, if you are using the a Fetch Request's fetch batch size property, accessing this count method above should not fault all of the objects. Reference: developer.apple.com/library/mac/#documentation/Cocoa/Referen‌​ce/…

[bobics]

@Senseful where does it say it won't fault the objects? It's not obvious from the docs. Is this something you tested?

[memmons]

@Senseful Also curious about the assertion that fetchedObjects count won't fire faults.

[pronebird]

@mokagio because performFetch already creates faults. Instead of looping through sections which can be incredibly expensive if you have thousands of them, you should simply call count on fetchedObjects.