Nil value for section in Core Data

Question

After some testing new features I faced a Core Data error which was really strange looking.

CoreData: error: (NSFetchedResultsController) A section returned nil value for section name key path 'date'. Objects will be placed in unnamed section

And if I scroll to the top of my UITableView I see cell with NULL values in it...

---

Let me introduce you to my situation. On the first (ever) viedDidLoad of this UITableView I download data from the server, parse it and load into Core Data. Pretty straight, huh? But everytime this viewDidLoad I check if there is something already stored in this entity and if so I scroll to the row which has nearest date to present date. To accomplish this I use method I've written:

- (void)scrollToNearestDateInFutureWithAnimation:(BOOL)animation
{
    // Saving present date for comparison purposes
    NSDate *presentDate = [NSDate date];
    // Making a big interval (2001)
    double interval = fabs([NSDate timeIntervalSinceReferenceDate]);

    // Getting managed object to hold the proper row
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Activity" inManagedObjectContext:self.moc];
    Activity *nearestActivity = [[Activity alloc] initWithEntity:entity insertIntoManagedObjectContext:self.moc];

    // Iterating each activity in fetched objects
    for (Activity *activity in [self.fetchedResultsController fetchedObjects]) {
        // Getting time interval between present date and activity start date
        double activityIntervalSincePresent = [activity.startDate timeIntervalSinceDate:presentDate];

        // Checing if interval is smaller than default one and is bigger than 0 (eliminating past dates)
        if (interval > activityIntervalSincePresent && activityIntervalSincePresent > 0) {
            interval = activityIntervalSincePresent;
            nearestActivity = activity;
        }
    }

    // Scrolling to the row
    [self.tableView scrollToRowAtIndexPath:[self.fetchedResultsController indexPathForObject:nearestActivity] atScrollPosition:UITableViewScrollPositionTop animated:animation];
}

And a part of viewDidLoad responsible for checking the existance of entity in Core Data:

if ([self coreDataHasEntriesForEntityName:@"Timetable"]) {
        // NSLog(@"Core Data has entries");
        NSError *error;
        if (![[self fetchedResultsController] performFetch:&error]) {
            // Update to handle the error appropriately.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        }

        // Scrolling to row with nearest date in future
        [self scrollToNearestDateInFutureWithAnimation:NO];

        // Checking for new timetable
        [self checkForTimetableUpdatesWithVersions:[self getTimetableVersions]];
    } else {
        // NSLog(@"No entries in Core Data");
        if ([self registeredTimetableExistsInUserDefaults]) {
            self.timetableID = [[NSUserDefaults standardUserDefaults] valueForKey:TIMETABLE_ID];
            [self showDownloadTimetableActionSheet];
        } else {
            [self showRegisterTimetableActionSheet];
        }
    }

For me, it seems like sometimes [[self fetchedResultsController] performFetch:&error] won't stop doing its job and I want it to scroll to the specific row... But I may be totally wrong with this guess. No more solutions come to my mind. Please help me!

Answer 1

This line is wrong for your purposes:

Activity *nearestActivity = [[Activity alloc] initWithEntity:entity insertIntoManagedObjectContext:self.moc];

because it is inserting an empty object into the data store that you don't want. You should just be doing:

Activity *nearestActivity = nil;

There seems to be a common misconception that you need to initialise a pointer with an object reference for it to be valid, but you don't, so don't, because it's wasteful (and in your case corruptive)