Question

I have 2 entities:

Performance.start (NSDate)    Location.coordinates
Performance.end   (NSDate)    Location.name_extern
Performance.location   <<-->  Location.performances

I have a NSFetchedResultsController for my UITableView set up with the following code:

[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                    managedObjectContext:self.managedObjectContext 
                                      sectionNameKeyPath:@"location.name_extern" 
                                               cacheName:nil];

So the data is divided into sections by locations (their names).

Now I have a variable selectedTime of type NSDate and want to fetch (with a single fetch if possible) the following:

1. Only 2 Performances per Location:
   • The Performance that is running (selectedTime BETWEEN {start, end})
   • The Performance that will start after the one that is running at the selected time

I’m really lost here :-/ Even if you could just give me the SQL statement for such a fetch/query I would at least know which direction to head..

Answer 1

Duh.. I think I found the final solution ..

The fetch is pretty simple:

NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:@"Performance" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

NSSortDescriptor *sort1 = [[NSSortDescriptor alloc] 
                          initWithKey:@"location.name_extern" ascending:YES];
NSSortDescriptor *sort2 = [[NSSortDescriptor alloc] 
                           initWithKey:@"start" ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:sort1,sort2,nil]];

[fetchRequest setFetchBatchSize:20];

NSFetchedResultsController *theFetchedResultsController = 
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                    managedObjectContext:self.managedObjectContext 
                                      sectionNameKeyPath:@"location.name_extern" 
                                               cacheName:nil];

With the following predicate:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"end > %@",selectedTime];

[fetchRequest setPredicate:predicate];

And here’s how I solved the “only 2 per location/section” part:

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
    if (selectedTime == nil)
    {
        return [sectionInfo numberOfObjects];
    }
    else
    {
        if ([sectionInfo numberOfObjects] > 2)
        {
            return 2;
        }
        else
        {
            return [sectionInfo numberOfObjects];
        }
    }
}

Thanks for trying though André!