iphone Core Data - Filtering NSFetchedResultController?

I was given a framework written by other programmers to access the core data. In this situation i receive a pre-loaded NSFetchedResultController which I need to filter, to display a part of it's data.

Here is what I tried:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"category==%@", @"current"];
[NSFetchedResultsController deleteCacheWithName:@"Root"];
[myResultController.fetchRequest setPredicat开发者_StackOverflowe:predicate];
myResultController.fetchedObjects = [myResultController.fetchedObjects filteredArrayUsingPredicate:predicate];

And i get an error saying that object cannot be set, either setter method is missing, or object is read-only.

So whats the best way to filter an NSFetchResultController which is already loaded, without having to store the filtered data into another array?

fetchedObjects is readonly. You cannot set it manualy.

What you need to do is to perform a new fetch with your myResultController.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"category==%@", @"current"];
[NSFetchedResultsController deleteCacheWithName:@"Root"];
[myResultController.fetchRequest setPredicate:predicate];
//myResultController.fetchedObjects = [myResultController.fetchedObjects filteredArrayUsingPredicate:predicate];
[myResultController performFetch:nil];