Question

I have two objects with a relationship in my Data Model…

1. Person {Name, position, Title}
2. Position {position, PositionSort}

Each of the above have their own class files (subclasses of NSManagedObject). I’m trying to sort by PositionSort above. I can currently sort by Position by using the following code.

NSSortDescriptor *sortDescriptorPosition = [[NSSortDescriptor alloc] initWithKey:@"position" ascending:YES];

I am unsure though how I’m able to access and use the PositionSort. Any ideas? Thanks!

UPDATE: Added full function…

- (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

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

    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sortDescriptorState = [[NSSortDescriptor alloc] initWithKey:@"position.positionSort" ascending:YES];

    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptorState, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];


    NSPredicate *searchPredicate = [NSPredicate predicateWithFormat:@"(companyID == %@)", company.companyID];
    [fetchRequest setPredicate:searchPredicate];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"position.positionDescription" cacheName:nil];

    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return __fetchedResultsController;
}

With the above code I’m getting the following error at Runtime.

2012-08-12 10:29:45.499 College[269:707] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSCFString 0xd6bd310> valueForUndefinedKey:]: this class is not key value coding-compliant for the key positionDescription.'

Answer 1

I’m not sure you want to sort exactly, but the following NSSortDescriptor can be used to sort the Person objects using the PositionSort value.

NSSortDescriptor *sortDescriptorPosition = [[NSSortDescriptor alloc] initWithKey:@"position.PositionSort" ascending:YES];

perhaps, you looked for this…