Question

I changed my core data model to a to-many relationship. I believe this is the correct model. I need to be able to do the following:

(1) A Meal can contain many Foods
(2) A Food iteme can be linked to many Meals

I get the following error with when I try to fetch all Foods for a certain Meal. This worked when it was a one-to-many, but not since I changed it to a to-many relationship.

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'to-many key not allowed here'

- (NSFetchedResultsController *)fetchedResultsController 
{       
    self.context = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 

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

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Food" inManagedObjectContext:self.context];

    [fetchRequest setEntity:entity];

    NSPredicate *foodPredicate = [NSPredicate predicateWithFormat:@"meals == %@", self.meal];
    [fetchRequest setPredicate:foodPredicate];

    NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    [fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
    [fetchRequest setFetchBatchSize:20];

    NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.context sectionNameKeyPath:nil cacheName:nil];


    self.fetchedResultsController = theFetchedResultsController;
    _fetchedResultsController.delegate = self;

    [fetchRequest release];
    [theFetchedResultsController release];

    return _fetchedResultsController;
}

Answer 1

Just the predicate needs to change, I think:

NSPredicate *foodPredicate = [NSPredicate predicateWithFormat:@"ANY meals == %@", self.meal];

since meals is now a set.