How to count unique dates of CoreData objects?

Question

I need a proper way to count how many unique days there are in CoreData objects with a property of type NSDate.

For example, I have the following:

<Object>.date = "2014-05-15 21:29:12 +0000";
<Object>.date = "2014-05-15 21:49:34 +0000";
<Object>.date = "2014-05-16 13:29:23 +0000";
<Object>.date = "2014-05-16 20:49:50 +0000";
<Object>.date = "2014-05-16 22:01:53 +0000";
<Object>.date = "2014-05-20 03:32:12 +0000";
<Object>.date = "2014-05-20 12:45:23 +0000";
<Object>.date = "2014-05-20 14:15:50 +0000";
<Object>.date = "2014-05-20 20:20:05 +0000";

In this case, the result must be 3 because there are 3 different days, 2014-05-15, 2014-05-16 and 2014-05-20

Any way to deal with this problem? I tried with NSPredicate but I did not succeed

Thanks!

Answer 1

That's easy. Let me show you what I'm going to do for it.

Group your results with sort description key. This example helps you to understand how it can be realized.

https://developer.apple.com/library/ios/samplecode/DateSectionTitles/Introduction/Intro.html

And then just calculate these groups.

EDIT:

NSDate+Utils.h

- (NSDate *) dateWithoutTime

NSDate+Utils.m

-(NSDate *) dateWithoutTime
{
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *components = [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit fromDate:self];
    return [calendar dateFromComponents:components];
}

some file

- (NSUInteger) someObjectsCount
{
    NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"SomeObject"];

    NSString *key = @"date.dateWithoutTime";

    fetchRequest.sortDescriptors = @[[[NSSortDescriptor alloc] initWithKey:key
                                                                 ascending:YES]];

    NSManagedObjectContext *context;
    context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];

    NSFetchedResultsController *aFetchedResultsController;
    aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                    managedObjectContext:context
                                                                      sectionNameKeyPath:key
                                                                               cacheName:nil];
    [aFetchedResultsController performFetch:nil];

    return [[aFetchedResultsController sections] count];
}

That's all!