Getting the count of a to-many relationship in core data

Question

I have a data model with a Parent entity and a child entity. The child entity has a to-many inverse relationship with Parent entity (a child can have multiple parents). I am currently trying to get the number of parents a particular child has:

Parent *doomedParent = [self.fetchedResultsController objectAtIndexPath:indexPath];

Child *child = [doomedParent valueForKey:@"child"];
int parentCount = [[child valueForKey:@"parents.@count"] intValue];

When trying to get the parents (Parent relationship) count from a child I get the following error:

'Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ valueForUndefinedKey:]: the entity Child is not key value coding-compliant for the key "parents.@count".'

Any ideas what I could be doing wrong?

Answer 1

You should be using -valueForKeyPath:, not -valueForKey:, which does not follow key paths (-valueForKey: is thus faster for single key lookups). This should work:

int parentCount = [[child valueForKeyPath:@"parents.@count"] intValue];

Answer 2

While Barry Wark's answer is correct for using KVC, is there any reason you don't just get the count of the .parents NSSet, like this:

NSUInteger parentCount = [child.parents count];

KVC is great and all, but unless I'm missing something, isn't it overkill for this situation?