RKCoreDataExample.m

// Cannot init an NSManagedObject. Have to insert into an NSManagedObjectContext instance.
NSManagedObjectSubclass * scratchObj = [NSEntityDescription insertNewObjectForEntityForName:@"Foo"
                                                                     inManagedObjectContext:AppDelegate.managedObjectContext];

// Set the properties on our object, e.g. via UITextField IBOutlets
scratchObj.foo = @"foo";

// Post the object. Assume use of an RKMapping here.
[[RKObjectManager sharedManager] postObject:scratchObj path:nil parameters:nil
   success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
     // mappingResult contains the resposne mapped to a new object. So won't there be two
     // instances of NSManagedObjectSubclass in my persistent store?
   } failure:nil];