Post JSON Body + MultiPart RestKit 0.2x fails - ios

Question

I am trying to post an object with an attached file.
NSMutableURLRequest *request =
[objectManager multipartFormRequestWithObject:reqDocObj
method:RKRequestMethodPOST
path:#"syncDocument.json"
parameters:nil
constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
[formData appendPartWithFileData:UIImagePNGRepresentation([UIImage imageNamed:#"graybox.png"])
name:#"image"
fileName:#"some_file"
mimeType:#"image/jpeg"];
}];
RKObjectRequestOperation *operation =
[objectManager
objectRequestOperationWithRequest:request
success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
}
failure:^(RKObjectRequestOperation *operation, NSError *error) {
NSLog(#"WS: errore operazione di richiesta %#",error);
}
];
[objectManager enqueueObjectRequestOperation:operation];
The objectManager is configured as:
[objectManager setAcceptHeaderWithMIMEType:RKMIMETypeJSON];
[objectManager setRequestSerializationMIMEType:RKMIMETypeJSON];
objectManager.requestSerializationMIMEType = RKMIMETypeJSON;
[EDIT]
My mapepd object is SynchDocObj:
requestDocMapping = [RKObjectMapping mappingForClass:[SynchDocObj class]];
[requestDocMapping addAttributeMappingsFromDictionary:mappingDocDict];
The problem is:
1) In the RKlogs, the request.body = null and the JSON object is put into the form-data
2) The server cannot decode the body because it is null
My question is:
1) Am I sending the JSON object in the wrong way?
2) If yes, how can I send a JSON object with a file upload, i.e. as a multipart request?
Regards!
[SOLUTION]
Following the suggestion of the answer, I think the solution is 1) retrieve the mapped object from the form-data and not the body ; 2) OR post a nil object and putting a JSON string within the form-data.

Answer 1

This:
[objectManager setRequestSerializationMIMEType:RKMIMETypeJSON];
objectManager.requestSerializationMIMEType = RKMIMETypeJSON;
is 2 different ways of saying the same thing - and you don't want to have either of them. You need to send the request as form URL encoded (the default value).
The easiest thing to do is to use the same form as in your current code to create the request, generate the JSON earlier and then use appendPartWithFormData:name: to add it to the request (just before you add the file).
To generate the JSON you can use RestKit (RKMappingOperation) or you can just create a dictionary / array of content and then use NSJSONSerialization to serialise that object to be added to the request.

Answer 2

Analyze my code, it works like a charm:
RKRequestDescriptor *requestDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:[FilledExamCard defineMapping] objectClass:[MappedClassName class] rootKeyPath:nil method:RKRequestMethodPUT];
NSData *jsonPayload = [self getJSONpayloadFromObject:mappedClassObject requestDescriptor:requestDescriptor];
NSURL *baseURL = [NSURL URLWithString:[ZDR_BASE_URL stringByAppendingString:#"PutExamCards"]];
AFHTTPClient *client = [AFHTTPClient clientWithBaseURL:baseURL];
[RKMIMETypeSerialization registerClass:[RKNSJSONSerialization class] forMIMEType:#"text/plain"];
[client setDefaultHeader:#"Accept" value:#"text/plain"];
RKObjectManager *objectManager = [[RKObjectManager alloc] initWithHTTPClient:client];
[objectManager setRequestSerializationMIMEType: RKMIMETypeJSON];
[objectManager addRequestDescriptor:requestDescriptor];
NSMutableURLRequest *request = [objectManager multipartFormRequestWithObject:nil method:RKRequestMethodPUT path:#"" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
// Name may vary depending from server settings
[formData appendPartWithFormData:jsonPayload name:#"model"];
}];
RKObjectRequestOperation *operation = [objectManager objectRequestOperationWithRequest:request success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
// Process data
} failure:^(RKObjectRequestOperation *operation, NSError *error) {
// An error occurred
}];
-(NSData*)getJSONpayloadFromObject:(NSObject*)object requestDescriptor:(RKRequestDescriptor*)requestDescriptor
{
NSDictionary *paramObject = [RKObjectParameterization parametersWithObject:object requestDescriptor:requestDescriptor error:nil];
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:paramObject options:NSJSONWritingPrettyPrinted error:&error];
return jsonData;
}