Cocoa Core Data efficient way to count entities

Question

I read much about Core Data.. but what is an efficient way to make a count over an Entity-Type (like SQL can do with SELECT count(1) ...). Now I just solved this task with s

Answer 1

It's really just this:

let kBoat = try? yourContainer.viewContext.count(for: NSFetchRequest(entityName: "Boat"))

"Boat" is just the name of the entity from your data model screen:

What is the global yourContainer?

To use core data, at some point in your app, one time only, you simply go

var yourContainer = NSPersistentContainer(name: "stuff")

where "stuff" is simply the name of the data model file.

You'd simply have a singleton for this,

import CoreData
public let core = Core.shared
public final class Core {
    static let shared = Core()
    var container: NSPersistentContainer!
    private init() {
        container = NSPersistentContainer(name: "stuff")
        container.loadPersistentStores { storeDescription, error in
            if let error = error { print("Error loading... \(error)") }
        }
    }
    
    func saveContext() {
        if container.viewContext.hasChanges {
            do { try container.viewContext.save()
            } catch { print("Error saving... \(error)") }
        }
    }
}

So from anywhere in the app

core.container

is your container,

So in practice to get the count of any entity, it's just

let k = try? core.container.viewContext.count(for: NSFetchRequest(entityName: "Boat"))