How to fetch managed objects sorted by calculated value
- by Marcin Zbijowski
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.
