NSFetchedResultsController didn't return data

I get stuck in some problem and after 2 days of seeking I've found solution but didn't get idea why does it work.

First, I'm initialized NSFetchedResultsController using following code (it look like a lot of automatically generated):

- (NSFetchedResultsController *)fetchedResultsController {

if (fetchedResultsController != nil)
    return fetchedResultsController;

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Profile"
                                          inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:20];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lastName" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc]
                                                         initWithFetchRequest:fetchRequest
                                                         managedObjectContext:self.managedObjectContext
                                                         sectionNameKeyPath:nil
                                                开发者_运维技巧         cacheName:@"Root"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
//[aFetchedResultsController performFetch:&error];

[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptors release];

return fetchedResultsController;

}

Have a look at commented string - there wasn't any of these strings and when I asked for data - I didn't get any (and it was there!). When I've uncommented that line, it starts work. Seems evident, but all examples I saw before hadn't that line. And they work. How can it be? I just want to know what am I doing wrong.

[aFetchedResultsController performFetch:&error]; has to be called at some point in order for the data to be fetched. The examples probably fetched the data at some point other than the accessor (it's fine in the accessor, though).