NSFetchedResultsController, Core data and Threading - objective-c

Question

Hello fellow overflowers
I have a hard time figuring out how to fetch NSManagedObjects in a background thread and then show the results via a NSFetchedResultsController.
This is my code so far:
_theManagedObjectContext = [[DataManager sharedInstance] mainManagedObjectContext];
__block NSMutableArray *objectsIDs;
[[[DataManager sharedInstance] backgroundManagedObjectContext] performBlock:^{
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = [NSEntityDescription entityForName:#"Ret" inManagedObjectContext:[[DataManager sharedInstance] backgroundManagedObjectContext]];
NSArray *results = [[[DataManager sharedInstance] backgroundManagedObjectContext] executeFetchRequest:fetchRequest error:nil];
for (Ret *ret in results) {
NSManagedObjectID *moID = [ret objectID];
[objectsIDs addObject:moID];
NSLog(#"%#", objectsIDs);
}
[[[DataManager sharedInstance] mainManagedObjectContext ] performBlock:^{
[self loadDishesWithObjectIDs:objectsIDs];
}];
}];
First I fetch all the objects in a background thread and then transfering the NSMangedObjectIDs to the main thread.
In my "loadDishes" method:
- (void)loadDishesWithObjectIDs:(NSArray *)objectsIDs {
/*
[NSFetchedResultsController deleteCacheWithName:#"dishes"];
self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:**???**? managedObjectContext:_theManagedObjectContext sectionNameKeyPath:nil cacheName:#"dishes"];
_fetchedResultsController.delegate = self;
NSError *error = nil;
if (![_fetchedResultsController performFetch:&error]) {
NSLog(#"Fetch Failed");
}
NSArray *theDishes = _fetchedResultsController.fetchedObjects;*/
}
How would I manage to show the objects with NSFetchResultscontroller by the ObjectIDs which is fetched from the background thread ?
Thank you in advance :)

Answer 1

You would need to create a fetch request that looks something like this
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = [NSEntityDescription entityForName:#"Ret"
inManagedObjectContext:[[DataManager sharedInstance] mainManagedObjectContext]];
fetchRequest.predicate = [NSPredicate predicateWithFormat:#"self IN %#", objectIDs];