sorting with fetched results controller causes section titles to be wrong

I'm using a fetchedResultsController to get data for a table view.

Here is the code for the fetchedController:

NSEntityDescription *entity = [NSEntityDescription 
                               entityForName:@"Appliance" inManagedObjectContext:context];
[fetchRequest setEntity:entity];

NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@开发者_运维知识库"name" ascending:NO];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];

[fetchRequest setFetchBatchSize:20];

NSFetchedResultsController *theFetchedResultsController = 
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest 
                                    managedObjectContext:context sectionNameKeyPath:@"productLine.name" 
                                               cacheName:@"Root"];

The section key path is using a related entity. Appliance <<--> ProductLine.

I'm getting the title for the sections in the table like this:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { 
    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo name];
}

This works just fine, but if I change the sorting to "ascending:YES" then the table sections get the wrong titles.

I found the answer myself. It turns out that I need to sort the results by productLine.name and then sort them by name. So I added another sort descriptor.

NSSortDescriptor *aSort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];

NSSortDescriptor *pSort = [[NSSortDescriptor alloc] initWithKey:@"productLine.name" ascending:YES];

[fetchRequest setSortDescriptors:[NSArray arrayWithObjects:pSort, aSort, nil]];

All is well now.