Hello,

I'm working on the app that uses CoreData. There is location entity that holds latitude and longitude values. I'd like to fetch those entities sorted by distance to the user's location. I tried to set sort descriptor to distance formula sqrt ((x1 - x2)^2 + (y1 - y2)^2) but it fails with exception "... keypath ... not found in entity".

NSString *distanceFormula = [NSString stringWithFormat:@"sqrt(((latitude - %f) * (latitude - %f)) + ((longitude - %f) * (longitude - %f)))", 
                            location.coordinate.latitude, 
                            location.coordinate.latitude, 
                            location.coordinate.longitude, 
                            location.coordinate.longitude];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:distanceFormula ascending:YES];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
NSError *error;
NSArray *result = [[self managedObjectContext] executeFetchRequest:fetchRequest error:&error];

I'd like to fetch already sorted objects rather then fetch them all and then sort in the code.

Any tips appreciated.