Core Data - sectionNameKeyPath with a One to Many Relationship

Question

I'm having difficulty creating tableView sections using a relationship.

I have two entities with a relationship List <----->> Item.

I want the List to be the sections and the Item to be the rows. I set the sectionNameKeyPath with a key path @"itemList". And here's what the rest of my fetchedResultsController looks like

- (NSFetchedResultsController *)fetchedResultsController {

    if (_fetchedResultsController != nil) {
        return _fetchedResultsController;
    }

    // Fetch Request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Item"];
    [fetchRequest setFetchBatchSize:20];

    // Sort Descriptors
    NSSortDescriptor *itemSort = [[NSSortDescriptor alloc] initWithKey:@"displayOrderItem" ascending:YES];
    NSSortDescriptor *sectionSort = [[NSSortDescriptor alloc] initWithKey:@"displayOrderList" ascending:YES];
    NSArray *sortDescriptors = @[sectionSort, itemSort];
    [fetchRequest setSortDescriptors:sortDescriptors];

    // Fetched Results Controller
    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"itemList" cacheName:nil];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

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

    return _fetchedResultsController;
}

The result is that the fetchedResultsController doesn't populate the tableView at all. When I try it without sections, with sectionNameKeyPath:nil and just setSortDescriptor:itemSort, it populates the tableView fine. Also, numberOfSectionsInTableView and controller didChangeSection is properly set up.

I'm not sure what I'm doing wrong. Can anybody help me with this?

Thanks

Answer 1

Change the section name key path to itemList.listName as the FRC is expecting a string name for the section, not a managed object 'representing' that section.