RestKit: per-request object mapping when using [[RKClient sharedClient] post: usingBlock:]
===

I need to POST a video to a server in the background. Until now i've been using this sort of pattern when POSTing:


    - (BOOL)loginUser:(user *)user
    {
        BOOL ret = NO;

        AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
        [appDelegate.waitView startWithMessage:@"Signing in ..."];

        [self.objectManager postObject:user usingBlock:^(RKObjectLoader *loader)
         {
             loader.delegate = self;
             loader.targetObject = nil;
         
             loader.objectMapping = [RKObjectMapping mappingForClass:[user class] usingBlock:^(RKObjectMapping *mapping)
                                 {
                                     [mapping mapKeyPath:@"id" toAttribute:@"ID"];
                                     [mapping mapKeyPath:@"last_name" toAttribute:@"last_name"];
                                     [mapping mapKeyPath:@"first_name" toAttribute:@"first_name"];
                                     [mapping mapKeyPath:@"middle_name" toAttribute:@"middle_name"];
                                     [mapping mapKeyPath:@"email" toAttribute:@"email"];
                                     [mapping mapKeyPath:@"password" toAttribute:@"password"];
                                     [mapping mapKeyPath:@"authentication_token" toAttribute:@"authentication_token"];
                                 }];
         
             loader.serializationMapping = [loader.objectMapping inverseMapping];
             loader.serializationMapping.rootKeyPath = NSStringFromClass([user class]);
         }];

        return ret;
    }

... but this pattern doesn't seem to let me access any RKRequest object on which to set the backgroundPolicy. So, i've looked at using RKClient like so:

    - (BOOL)postBigMediaFile:(NSString *)pathToBigFile
    {
        BOOL ret = NO;
    
        NSString *resourcePath = @"/bigFile";
 
        [[RKClient sharedClient] post:resourcePath usingBlock:^(RKRequest *request)
         {
             request.backgroundPolicy = RKRequestBackgroundPolicyContinue;

             // how do I set up the object mapping?


         }];
    
        return ret;
    }

... but the RKRequest object doesn't seem to have a way of accessing an RKObjectLoader for which to setup the mapping on. How do I post data in the background using object mapping?

