Rails RestKit POST request json's root class missing - objective-c

Question

I had this previous problem which I fixed, but I know the fix is def not done the right way. Can some one point me in the right direction for the right fix?
Basically I create a object with iOS sim via RESTkit postObject, and I got this message:
Processing PeopleController#create (for 127.0.0.1 at 2012-01-13 03:55:46) [POST]
Parameters: {"name"=>"data"}
Person Create (0.4ms) INSERT INTO "people" ("created_at", "updated_at", "name")
VALUES('2012-01-13 11:55:46', '2012-01-13 11:55:46', NULL)
Completed in 27ms (View: 1, DB: 0) | 200 OK
A nice gentlemen pointed out that my class inside my create function is only accepting a :person class which I overlooked.
def create
#person = Person.new(params[:person]) , thus looking for {"person" => {"name"=>"data"}}
I fixed this by doing
#person =Person.new(name:=>params[:name]) since i am only sending {"name"=>"data"}
now it creates ok, and I can see the entry on my ios sim. But I know this is not the right way. The right way should be {"person" => {"name"=>"data"}} sent in to the original function. Plus I get an error could not find an object mapping for keyPath:". Any thoughts?
Here is my xcode:
#interface Data: NSObject{// imaginary over arching class
Person * person;
NSArray *dog;
#property (nonatomic, retain) Person * person;
#property (nonatomic, retain) NSArray * dog;
#interface Data : NSObject {
Person *person;
NSArray *dogs;
}
#property (nonatomic ,retain) Person *person;
#property (nonatomic ,retain) NSArray *dogs;
#end
#interface Person : NSObject {
NSString *name;
NSNumber *personId;
NSDate *updatedAt;
NSDate *createdAt;
}
#property (nonatomic , retain) NSDate * createdAt;
#property (nonatomic , retain) NSDate * updatedAt;
#property (nonatomic , retain) NSNumber *personId;
#property (nonatomic , retain) NSString *name;
#end
RKObjectMapping* userMapping = [RKObjectMapping mappingForClass:[Person class]];
[userMapping mapKeyPath:#"created_at" toAttribute:#"createdAt"];
[userMapping mapKeyPath:#"updated_at" toAttribute:#"updatedAt"];
[userMapping mapKeyPath:#"name" toAttribute:#"name"];
[userMapping mapKeyPath:#"id" toAttribute:#"personId"];
RKObjectMapping* dogMapping = [RKObjectMapping mappingForClass:[Dog class]];
[dogMapping mapKeyPath:#"created_at" toAttribute:#"createdAt"];
[dogMapping mapKeyPath:#"person_id" toAttribute:#"spersonId"];
[dogMapping mapKeyPath:#"name" toAttribute:#"name"];
[dogMapping mapKeyPath:#"updated_at" toAttribute:#"updatedAt"];
[dogMapping mapKeyPath:#"id" toAttribute:#"dogId"];
RKObjectMapping *dataMapping = [RKObjectMapping mappingForClass:[Data class]];
[dataMapping mapKeyPath:#"dog" toAttribute:#"dogs"];
[dataMapping mapKeyPath:#"person" toRelationship:#"person" withMapping:userMapping];
[[RKObjectManager sharedManager].mappingProvider addObjectMapping:dataMapping];
[[RKObjectManager sharedManager] loadObjectsAtResourcePath:#"/people"
objectMapping:dataMapping delegate:self];
RKObjectRouter * router = [RKObjectManager sharedManager].router;
[router routeClass: [Person class] toResourcePath:#"/people/:personId"];
[router routeClass: [Person class] toResourcePath:#"/people"
forMethod:RKRequestMethodPOST];
RKObjectMapping *personSerializationMapping = [RKObjectMapping mappingForClass:
[NSMutableDictionary class]];
[personSerializationMapping attribute:#"name", nil];
[RKObjectManager sharedManager].mappingProvider
setSerializationMapping:personalSerializationMapping forClass: [Person class]];
Person *dave = [[Person alloc]init];
dave.name = #"Dave";
[[RKObjectManager sharedManager] postObject:dave delegate:self];
}

Answer 1

Take Person as an example:
RKObjectMapping* userMapping = [RKObjectMapping mappingForClass:[Person class]];
[userMapping mapKeyPath:#"created_at" toAttribute:#"createdAt"];
[userMapping mapKeyPath:#"updated_at" toAttribute:#"updatedAt"];
[userMapping mapKeyPath:#"name" toAttribute:#"name"];
[userMapping mapKeyPath:#"id" toAttribute:#"personId"];
To config RestKit to POST with a root path, replace:
[[[RKObjectManager sharedManager] mappingProvider]
setSerializationMapping:personalSerializationMapping
forClass:[Person class]];
with:
[[[RKObjectManager sharedManager] mappingProvider]
registerMapping:objectMapping
withRootKeyPath:#"person"];
Now Rails will receive {"person" => {"name"=>"data"}} instead of {"name"=>"data"}.
For reference, here is the magic of registerMapping:
- (void)registerObjectMapping:(RKObjectMapping *)objectMapping withRootKeyPath:(NSString *)keyPath {
// TODO: Should generate logs
objectMapping.rootKeyPath = keyPath;
[self setMapping:objectMapping forKeyPath:keyPath];
RKObjectMapping* inverseMapping = [objectMapping inverseMapping];
inverseMapping.rootKeyPath = keyPath;
[self setSerializationMapping:inverseMapping forClass:objectMapping.objectClass];
}
it does both setMapping and setSerializationMapping with the clever [objectMapping inverseMapping] trick.

Answer 2

Yea finally figured it out. The mapping was wrong. Instead of addObjectMapping: dataMapping, it should have been userMapping with keyPath person which is userMapping. btw thnx #favo for editing my chicken scratch =] now it can GET and POST fine!

Answer 3

For completionist sake, the error about "could not find mapping for key path ''" seems to be a thing with Rails create action.
There's a good answer for this problem in this SO question: how to post an object to Rails using RESTKit