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

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 2

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 3

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;