How to Efficiently Reset Attributes in a Core Data Entity
for (Deck *deck in self.deckArray) {
        if ([deck.beenSeen isEqualToNumber:[NSNumber numberWithInt:1]]) {
            [deck setBeenSeen:[NSNumber numberWithInt:0]];
            [self.managedObjectContext save:&error];
        }
    }

for (Deck *deck in self.deckArray) {
    if ([deck.beenSeen isEqualToNumber:[NSNumber numberWithInt:1]]) {
        [deck setBeenSeen:[NSNumber numberWithInt:0]];
    }
}
[self.managedObjectContext save:&error];

for (Deck *deck in self.deckArray) {
    [deck setBeenSeen:[NSNumber numberWithInt:0]];
    }
    [self.managedObjectContext save:&error];
}

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"beenSeen == %@",
                          [NSNumber numberWithInt:1]];

NSArray* filtered = [self.deckArray filteredArrayUsingPredicate:predicate];

[filtered setValue:[NSNumber numberWithInt:0] forKeyPath:@"beenSeen"];

[self.managedObjectContext save:&error];