Restkit post with nested objects - ios

Question

Hi I'm new to using restkit and I'm confused on how to post nested objects. I am trying to post the following json:
{
"user": {
"id": "77777-795C-4374-9A29-5C12FF8031F7",
"firstname:": "joe",
"lastname": "bob"
},
"device": {
"token": "phPS2sxbRRvoBbdE8e1VT8nFIJ4R8aJ6rdoCJ8iP1luWm3gUJDMnRHBs1SarfosTsIeYMMxwraLCY35B4whaFIISdosHzqa96vkZANHFy5rusHcrnUQuFgJHnsnqOsgxgOPd8QbrZAAxIlmqCt0an5pH69PWZAXcOVuzFilo310oeNW04qWZCWb8GWYMkODcMuUZANCAAFfvZB4ZAyokBADz"
}
}
I am using Restkit version 0.20.3
This is what my mapping looks like:
RKObjectMapping *userMapping = [RKObjectMapping requestMapping];
[userMapping addAttributeMappingsFromDictionary:#{
#"id": #"id",
#"firstname": #"firstname",
#"lastname": #"lastname"
}];
RKObjectMapping *deviceMapping = [RKObjectMapping requestMapping];
[facebookMapping addAttributeMappingsFromDictionary:#{
#"token": #"token"
}];
RKObjectMapping *authMapping = [RKObjectMapping requestMapping];
[authMapping addPropertyMapping:[RKRelationshipMapping
relationshipMappingFromKeyPath:#"user"
toKeyPath:#"user"
withMapping:userMapping]];
[authMapping addPropertyMapping:[RKRelationshipMapping
relationshipMappingFromKeyPath:#"device"
toKeyPath:#"device"
withMapping:deviceMapping]];
RKRequestDescriptor *authDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:authMapping objectClass:[AuthCredentials class] rootKeyPath:nil method:RKRequestMethodPOST];
[manager addRequestDescriptor:authDescriptor];
User *user = [[User alloc] init];
user.id = #"77777-795C-4374-9A29-5C12FF8031F7";
user.firstname = #"joe";
user.lastname = #"bob";
Device *device = [[Device alloc] init];
device.token = #"phPS2sxbRRvoBbdE8e1VT8nFIJ4R8aJ6rdoCJ8iP1luWm3gUJDMnRHBs1SarfosTsIeYMMxwraLCY35B4whaFIISdosHzqa96vkZANHFy5rusHcrnUQuFgJHnsnqOsgxgOPd8QbrZAAxIlmqCt0an5pH69PWZAXcOVuzFilo310oeNW04qWZCWb8GWYMkODcMuUZANCAAFfvZB4ZAyokBADz";
AuthCredentials *cred = [[AuthCredentials alloc] init];
cred.user = user;
cred.device = device;
[manager postObject:cred path:#"/testpost" parameters:nil
success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult)
{
}
failure:^(RKObjectRequestOperation *operation, NSError *error)
{
}];
My error message is the following:
Error Domain=org.restkit.RestKit.ErrorDomain Code=1001 "No mappable object representations were found at the key paths searched." UserInfo=0x9427070 {DetailedErrors=(
), NSLocalizedFailureReason=The mapping operation was unable to find any nested object representations at the key paths searched:
The representation inputted to the mapper was found to contain nested object representations at the following key paths: error
This likely indicates that you have misconfigured the key paths for your mappings., NSLocalizedDescription=No mappable object representations were found at the key paths searched., keyPath=null}