Core data objects update through loop - ios

Question

I have a tableView showing core-data objects. On the same view there are five buttons. Each button action should update the value of an attribute from the objects.
As an example, I will show you what I have to update the attribute 'isDone':
- (IBAction)allDoneAction:(id)sender {
NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
int i=0;
for (NSManagedObject *mo in context)
{
[mo setValue:#"Done" forKey:#"isDone"];i++;
}
[managedObjectContext save:nil];
}
This method throws following following exception:
NSManagedObjectContext countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0x9a6b0a0
2014-01-06 19:01:43.862 To-Do Pro[679:a0b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSManagedObjectContext countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0x9a6b0a0'
What do I need to avoid the exception and obtain the desired update?
Here is my NSFetchedResultsController:
- (NSFetchedResultsController *)fetchedResultsController
{
if (fetchedResultsController) return fetchedResultsController;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity =
[NSEntityDescription entityForName:#"FavoriteThing"
inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
NSSortDescriptor *sortDescriptor =
[[NSSortDescriptor alloc] initWithKey:#"displayOrder"
ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc]
initWithObjects:sortDescriptor, nil];
//SOLO TO-DOS DE TODAY
todayDate = [NSDate date];
NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit fromDate:todayDate]; // Get necessary date components
NSNumber *yearBuscado = [NSNumber numberWithLong:[components year]];
NSNumber *mesBuscado = [NSNumber numberWithLong:[components month]];
NSNumber *diaBuscado = [NSNumber numberWithLong:[components day]];
// NSString *tipourgente = #"Urgent";
// NSString *tipocolor = #"Yellow";
NSString *textoNotDone = #"Not done";
NSString *textoNotDeleted = #"Not deleted";
NSPredicate *yearPredicate = [NSPredicate predicateWithFormat:#"todoYear == %#", yearBuscado];
NSPredicate *monthPredicate = [NSPredicate predicateWithFormat:#"todoMonth == %#", mesBuscado];
NSPredicate *dayPredicate = [NSPredicate predicateWithFormat:#"todoDay == %#", diaBuscado];
NSPredicate *notDonePredicate = [NSPredicate predicateWithFormat:#"isDone== %#", textoNotDone];
NSPredicate *notDeletedPredicate = [NSPredicate predicateWithFormat:#"isSemiDeleted==%#", textoNotDeleted];
// NSPredicate *urgentPredicate = [NSPredicate predicateWithFormat:#"urgent == %#", tipourgente];
// NSPredicate *colorPredicate = [NSPredicate predicateWithFormat:#"color == %#", tipocolor];
[fetchRequest setSortDescriptors:sortDescriptors];
NSPredicate *busqueda = [NSCompoundPredicate andPredicateWithSubpredicates:#[yearPredicate,monthPredicate,dayPredicate,notDonePredicate,notDeletedPredicate]];
[fetchRequest setPredicate:busqueda];
NSFetchedResultsController *aFetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:managedObjectContext
sectionNameKeyPath:nil cacheName:nil];
aFetchedResultsController.delegate = self;
[self setFetchedResultsController:aFetchedResultsController];
[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptors release];
return fetchedResultsController;
}

Answer 1

Ok, I know absolutely nothing about core data, but from what I have researched in the last two minutes it appears as though you do not loop over An object of NSManagedObjectContext. You need to create a search within the context and get the results from that. Then iterate through the results and modify willy nilly.
Here is an example taken from this answer:
NSManagedObjectContext * context = [self managedObjectContext];
NSFetchRequest * fetch = [[[NSFetchRequest alloc] init] autorelease];
[fetch setEntity:[NSEntityDescription entityForName:#"ShoppingBasket" inManagedObjectContext:context]];
NSArray * result = [context executeFetchRequest:fetch error:nil];
for (id basket in result)
[context deleteObject:basket];
So get the context, Create a search, get an array from the context based on the search criteria, loop through the results and do as you will with updating them.

Answer 2

If you are using a fetchedResultsController already to populate the tableView then you can iterate over the objects in the fetchedResultsController like this:
- (IBAction)allDoneAction:(id)sender {
NSArray *objects = [fetchedResultsController fetchedObjects];
for (NSManagedObject *mo in objects) {
[mo setValue:#"Done" forKey:#"isDone"];i++;
}
NSError *error;
bool result = [[fetchedResultsController managedObjectContext] save:&error];
if (!result) {
NSLog(#" error saving context, %#, %#", error, error.userInfo);
}
}
BTW you should be checking for errors in your call to save so don't pass in nil.