gistfile1.m

// as NSObject
RKObjectMapping* mapping = [RKObjectMapping mappingForClass:[TestMappable class]]; 
[mapping mapKeyPath:@"numbers" toAttribute:@"orderedSet"]; 
TestMappable* object = [[[TestMappable alloc] init] autorelease]; 

id<RKParser> parser = [[RKParserRegistry sharedRegistry] parserForMIMEType:@"application/json"]; 
id data = [parser objectFromString:@"{\"numbers\":[1, 2, 3]}" error:nil]; 

RKObjectMappingOperation* operation = [[RKObjectMappingOperation alloc] initWithSourceObject:data destinationObject:object mapping:mapping]; 
BOOL success = [operation performMapping:nil]; 

// as NSManagedObject
RKManagedObjectMapping* catMapping = [RKManagedObjectMapping mappingForClass:[RKCat class]]; 
catMapping.primaryKeyAttribute = @"railsID"; 
[catMapping mapAttributes:@"name", nil]; 

NSDictionary* mappableData = [NSDictionary dictionaryWithKeysAndObjects:@"name", @"Natasha", @"railsID",  [NSNumber numberWithInt:31337], nil]; 
RKCat* cat = [RKCat object]; 
RKManagedObjectMappingOperation* operation = [[RKManagedObjectMappingOperation alloc] initWithSourceObject:mappableData destinationObject:cat mapping:catMapping];
BOOL success = [operation performMapping:nil];