Question

I have a NSFetchRequest (executing in a NSFetchedResultsController) for the following data:

Person (one-to-many) Encounter

Encounter has an int field “type”. In my tableView, I want to show:

Person A - Encounter of type 1
Person A - Encounter of type 2
Person B - Encounter of type 1

etc. That is, for a Person, I only want one Encounter of each type. Is there a way to do that in a Core Data query? I could do this with code to filter the result of an NSFetchRequest, but then I couldn’t use NSFetchedResultsController.

[EDIT]

Here’s the code I’m currently trying. The result is several Encounters with the same type for one Person.

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// entity
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Encounter" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

// return distinct
NSDictionary *entityProperties = [entity propertiesByName];
[fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:
                                    [entityProperties objectForKey:@"person"], 
                                    [entityProperties objectForKey:@"type"], 
                                    nil]];
[fetchRequest setReturnsDistinctResults:YES];

[fetchRequest setResultType:NSDictionaryResultType];

NSError *error;
NSArray *fetchedObjects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];

for (NSDictionary *d in fetchedObjects) {
    NSLog(@"NSDictionary = %@", d);
}

[fetchRequest release];

Answer 1

I am assuming you want to return just one record for each type of Encounter even if a Person has more than one of any given type. You can accomplish this by adjusting your NSFetchRequest accordingly:

[fetchRequest setReturnsDistinctValues:YES];