Group By for Core Data Results - ios

Question

I am using Core Data and generally, I have a Game, a Game Phase, and points scored for different types of actions (lets say pointsA, pointsB).
Each game consists of two phases and there are hence for each player a total points per phase and then per game (phase 1 + phase 2).
My Score Entity in Core Data has:
Player (Relationship to player),
Game (Relationship to game),
Phase (attribute),
PointsA (attribute),
PointsB (attribute).
So each player has a record for a Score in a Phase in a Game.
In order to get in fetch all points for a given player AGGREGATED BY GAME (so SQL equivalent of "Group By"). I managed to use this code and IT WORKS:
CODE:
NSError *error;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = [NSEntityDescription entityForName:#"Score" inManagedObjectContext:self.managedObjectContext];
fetchRequest.predicate=[NSPredicate predicateWithFormat:#"player == %#",_currentPlayer];
NSExpressionDescription* ex = [[NSExpressionDescription alloc] init];
[ex setExpression:[NSExpression expressionWithFormat:#"#sum.pointsA"]];
[ex setExpressionResultType:NSDecimalAttributeType];
[ex setName:#"pointsA"];
NSExpressionDescription* ex2 = [[NSExpressionDescription alloc] init];
[ex2 setExpression:[NSExpression expressionWithFormat:#"#sum.pointsB"]];
[ex2 setExpressionResultType:NSDecimalAttributeType];
[ex2 setName:#"pointsB"];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:#"Game",ex, ex2,nil]];
[fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObjects:#"Game",nil]];
[fetchRequest setResultType:NSDictionaryResultType ];
results= [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
My question is: Suppose I have MANY MORE POINTS TYPES, as in pointsC, PointsD, etc.. (let's say scores for many more different kinds of actions). Do I have to use a SEPARATE NSExpressionDescription (ex and ex2 above) for all of these ?
Is this really how long winded it is in Core Data? Is there a quicker way?
I am relatively new to Core Data.
For those who are wondering how to parse through the results set:
for (id Res in results) {
NSLog(#"pointsA: %# ", Res[#"pointsA"] );
NSLog(#"pointsB: %# ", [Res valueForKey:#"pointsB"] );
//both work
}

Answer 1

OK, answering my own question: I guess a more elegant way would be to feed in an array of items with the Core Data attribute names, which can then be as long as you want:
(NSArray*)items contains pointsA, pointsB, pointsC, pointsD, all the way to z and beyond if you so require.
///Code///
-(void)fetchRes:(NSArray*)items
{
NSError *error;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = [NSEntityDescription entityForName:#"Score" inManagedObjectContext:self.managedObjectContext];
fetchRequest.predicate=[NSPredicate predicateWithFormat:#"player == %#",_currentPlayer];
NSMutableArray *propsArray=[[NSMutableArray alloc]initWithObjects:#"Game", nil];
for (int i=0;i<items.count;i++)
{
NSString *desc=[[NSString alloc]initWithFormat:#"#sum.%#",items[i]];
NSExpressionDescription* ex3 = [[NSExpressionDescription alloc] init];
[ex3 setExpression:[NSExpression expressionWithFormat:desc]];
[ex3 setExpressionResultType:NSDecimalAttributeType];
[ex3 setName:items[i]];
[propsArray insertObject:ex3 atIndex:i+1];
}
[fetchRequest setPropertiesToFetch:propsArray];
[fetchRequest setPropertiesToGroupBy:[NSArray arrayWithObjects:#"Game",nil]];
[fetchRequest setResultType:NSDictionaryResultType ];
results=[self.managedObjectContext executeFetchRequest:fetchRequest error:&error] ;
}
Not sure what the performance / memory consequences are ?