NSFetchedResultsController always returns NSManagedObject objects instead of custom

Question

Hi there,

I am using CoreData and have an Entity ContactList defined, which I created using the XCode xcdatamodel tool (or whatever you call that built-in thing:). I also set the Entity's Class name to "ContactList". I then used rentzsch's mogenerator (http://github.com/rentzsch/mogenerator) to generate my custom class files and added the simple method "toString" to my ContactList class.

The fetchedResultsController callback is pretty much standard and looks as follows:

- (NSFetchedResultsController *)fetchedResultsController {

if (fetchedResultsController_ != nil) {
    return fetchedResultsController_;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"ContactList" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:20];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptors release];

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

return fetchedResultsController_;
}    

Now, when I start my application and try to call that method on a "ContactList" object, which in turn I get from a NSFetchedResultsController, I get

ContactList *contactList = (ContactList *) [self.fetchedResultsController objectAtIndexPath:indexPath];
[contactList toString];    
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSManagedObject toString]: unrecognized selector sent to instance 0x6af7bf0'

As the message shows, somehow the NSFetchedResultsController does not return a "ContactList" object, but a more general NSManagedObject instead.

Does anybody know why and how to resolve this???

Answer 1

Ok, I figured this it out.

The problem was that the mogenerator script did not add its generated source files to the project's compile target. This way the classes never got compiled and included (I wonder how it worked without any model object classes :)

After adding the .xcdatamodel file to the Target (RightClick on .xcdatamodel file -> Targets -> check your project) everything works now.

For further info go here