Cocoa Core Data efficient way to count entities - objective-c

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 selecting all with NSFetchedResultsController and getting the count of the NSArray! I am sure this is not the best way...

Answer 1

I don't know whether using NSFetchedResultsController is the most efficient way to accomplish your goal (but it may be). The explicit code to get the count of entity instances is below:
// assuming NSManagedObjectContext *moc
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:entityName inManagedObjectContext:moc]];
[request setIncludesSubentities:NO]; //Omit subentities. Default is YES (i.e. include subentities)
NSError *err;
NSUInteger count = [moc countForFetchRequest:request error:&err];
if(count == NSNotFound) {
//Handle error
}
[request release];

Answer 2

To be clear, you aren't counting entities, but instances of a particular entity. (To literally count the entities, ask the managed object model for the count of its entities.)
To count all the instances of a given entity without fetching all the data, the use -countForFetchRequest:.
For example:
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity: [NSEntityDescription entityForName: entityName inManagedObjectContext: context]];
NSError *error = nil;
NSUInteger count = [context countForFetchRequest: request error: &error];
[request release];
return count;

Answer 3

Swift
It is fairly easy to get a count of the total number of instances of an entity in Core Data:
let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
let fetchRequest = NSFetchRequest(entityName: "MyEntity")
let count = context.countForFetchRequest(fetchRequest, error: nil)
I tested this in the simulator with a 400,000+ object count and the result was fairly fast (though not instantaneous).

Answer 4

I'll just add that to make it even more efficient... and because its just a count, you don't really need any property value and certainly like one of the code examples above you don't need sub-entities either.
So, the code should be like this:
int entityCount = 0;
NSEntityDescription *entity = [NSEntityDescription entityForName:#"YourEntity" inManagedObjectContext:_managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:entity];
[fetchRequest setIncludesPropertyValues:NO];
[fetchRequest setIncludesSubentities:NO];
NSError *error = nil;
NSUInteger count = [_managedObjectContext countForFetchRequest: fetchRequest error: &error];
if(error == nil){
entityCount = count;
}
Hope it helps.

Answer 5

I believe the easiest and the most efficient way to count objects is to set NSFetchRequest result type to NSCountResultType and execute it with NSManagedObjectContext countForFetchRequest:error: method.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:entityName];
fetchRequest.resultType = NSCountResultType;
NSError *fetchError = nil;
NSUInteger itemsCount = [managedObjectContext countForFetchRequest:fetchRequest error:&fetchError];
if (itemsCount == NSNotFound) {
NSLog(#"Fetch error: %#", fetchError);
}
// use itemsCount

Answer 6

I wrote a simple utility method for Swift 3 to fetch the count of the objects.
static func fetchCountFor(entityName: String, predicate: NSPredicate, onMoc moc: NSManagedObjectContext) -> Int {
var count: Int = 0
moc.performAndWait {
let fetchRequest: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest(entityName: entityName)
fetchRequest.predicate = predicate
fetchRequest.resultType = NSFetchRequestResultType.countResultType
do {
count = try moc.count(for: fetchRequest)
} catch {
//Assert or handle exception gracefully
}
}
return count
}

Answer 7

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"))

Answer 8

In Swift 3
static func getProductCount() -> Int {
let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Product")
let count = try! moc.count(for: fetchRequest)
return count
}

Answer 9

If you want to find count for specific predicated fetch, i believe this is the best way:
NSError *err;
NSUInteger count = [context countForFetchRequest:fetch error:&err];
if(count > 0) {
NSLog(#"EXIST");
} else {
NSLog(#"NOT exist");
}

Answer 10

Swift 5 solution:
var viewContext: NSManagedObjectContext!
do {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "insertName")
let count = try viewContext.count(for: fetchRequest)
print("Counted \(count) objects")
}
catch {
print("Error")
}