iOS Core Data KeyValue Coding with to-many Relationships

[seepel]

I have an entity (parent) with a field (name) and a to-many relationship (child). What I would ultimately like to get is a fetch like

SELECT name, count(*) 
FROM parent 
JOIN child 
ON parent.pk = child.parent_fk 
GROUP by name 
ORDER by count(*) DESC;

So that it would output something like this

Parent_1|193
Parent_2|44
Parent_3|31
Parent_4|31
Parent_5|30
Parent_6|25

My first attempt was to do something along the lines of (assume I have a valid NSManagedObjectContext named context ... because I do)

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"parent" inManagedObjectContext:context];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"child.@count" ascending:NO];
request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
NSError *error;
NSArray *results = [context executeFetchRequest:request error:&error];
NSArray *parents = [results valueForKey:@"name"];
NSArray *numberOfChildren = [results valueForKey:@"child.@count"];
[request release];
[sortDescriptor release];

I expected I would get an NSArray parents with the content from the first column of my SQL statement, and an NSArray numberOfChildren with the content from the second column of my SQL statement. Instead I got an exception

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Keypath containing KVC aggregate where there shouldn't be one; failed to handle child.@count'

I also tried the reverse

@count.child

and got the exception

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath @count.child not found in entity <NSSQLEntity parent id=3>'

Does anyone have a suggestion as to how I could procede? I'd like to not fault in the child entities which I thought would be possible through this method.

Thanks