title: Mapping with Restkit 0.20 this class is not key value coding-compliant for the key
body: <p>Hello I am having problem mapping data from the api using restkit. I have this below data. I really appreciate anyone who can point out my mistake.</p>
  
  <pre><code>{"GameId":1,"Items":
  
  [{"Id":1,"PicUrl":"someurlhere","Answers":
  
  ["Paris","New York","San Francisco","Rome"],"CorrectAnswer":"San Francisco","Categories"}]}
  </code></pre>
  
  <p>And this is how i am planning to store the data at the client side:</p>
  
  <pre><code>#import &lt;Foundation/Foundation.h&gt;
  
  GameObjects.h
  
      @interface GameObjects : NSObject
      @property(nonatomic, strong)NSNumber *GameId;
      @property(nonatomic,strong)NSMutableArray *Items;
      @property(nonatomic,strong)NSNumber *IId;
      @property(nonatomic,strong)NSURL *PicUrl;
      @property(nonatomic,strong)NSMutableArray *Answers;
      @property(nonatomic,strong)NSString *CorrectAnswer;
      @property(nonatomic,strong)NSString *CategoryName;
      @end
  
  
  
  GameObjects.m
  
  #import "GameObjects.h"
  
  @implementation GameObjects
  @synthesize GameId;
  @synthesize Items;
  @synthesize Answers;
  @synthesize IId;
  @synthesize CategoryName;
  @synthesize CorrectAnswer;
  @synthesize PicUrl;
  - (id)init
  {
      self = [super init];
      if (self) {
  
          Items = [[NSMutableArray alloc]initWithObjects:PicUrl,Answers,CorrectAnswer,CategoryName, nil];
  
      }
      return self;
  }
  
  @end
  </code></pre>
  
  <p>ANd this is how I do the mapping:</p>
  
  <pre><code>-(void)viewDidLoad
  {
  
      //restkit
      RKObjectMapping *GameMapping = [RKObjectMapping mappingForClass:[GameObjects class]];
  
      [GameMapping addAttributeMappingsFromDictionary:@{   @"GameId":@"GameId",
                                                           @"Items": @"Items",
                                                           @"Id": @"Id",
                                                           @"PicUrl": @"PicUrl",
                                                           @"Answers":@"Answers",
                                                           @"CorrectAnswer":@"CorrectAnswer",
                                                           @"CategoryName":@"CategoryName"
                                                           }];
  
      RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:GameMapping method:RKRequestMethodGET pathPattern:nil keyPath:@"GameId" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
      NSURL *URL = [NSURL URLWithString:@"someurlhere"];
      NSURLRequest *request =[NSURLRequest requestWithURL:URL];
      RKObjectRequestOperation *objectRequestOperation = [[RKObjectRequestOperation alloc]initWithRequest:request responseDescriptors:@[responseDescriptor]];
      [objectRequestOperation setCompletionBlockWithSuccess:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
          RKLogInfo(@"Load collection of Articles: %@", mappingResult.array);
      } failure:^(RKObjectRequestOperation *operation, NSError *error) {
          RKLogError(@"Operation failed with error: %@", error);
      }];
      [objectRequestOperation start];
  
  
  }
  </code></pre>
  
  <p>And my output:</p>
  
  <pre><code>2013-09-30 14:28:04.204 FlickRest[3826:a0b] I restkit:RKLog.m:34 RestKit logging initialized...
  2013-09-30 14:28:04.478 FlickRest[3826:a0b] ViewController - viewDidLoad
  2013-09-30 14:28:12.158 FlickRest[3826:a0b] I restkit.network:RKObjectRequestOperation.m:180 GET 'someurlhere'
  
  2013-09-30 14:28:18.243 FlickRest[3826:1a07] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[&lt;__NSCFNumber 0x8e20580&gt; valueForUndefinedKey:]: this class is not key value coding-compliant for the key GameId.'
  *** First throw call stack:
  (
      0   CoreFoundation                      0x020ca5e4 __exceptionPreprocess + 180
      1   libobjc.A.dylib                     0x01e4d8b6 objc_exception_throw + 44
      2   CoreFoundation                      0x0215a6a1 -[NSException raise] + 17
      3   Foundation                          0x00c95b0a -[NSObject(NSKeyValueCoding) valueForUndefinedKey:] + 282
      4   Foundation                          0x00c02b61 _NSGetUsingKeyValueGetter + 81
      5   Foundation                          0x00c0219b -[NSObject(NSKeyValueCoding) valueForKey:] + 260
      6   Foundation                          0x00c21c9a -[NSObject(NSKeyValueCoding) valueForKeyPath:] + 409
      7   FlickRest                           0x0007fc31 -[RKMappingSourceObject valueForKeyPath:] + 833
      8   FlickRest                           0x00085247 -[RKMappingOperation applyAttributeMappings:] + 1671
      9   FlickRest                           0x0008cc3e -[RKMappingOperation main] + 4062
      10  Foundation                          0x00ca9a69 -[__NSOperationInternal _start:] + 671
      11  Foundation                          0x00c26798 -[NSOperation start] + 83
      12  FlickRest                           0x0007a2c5 -[RKMapperOperation mapRepresentation:toObject:atKeyPath:usingMapping:metadata:] + 1957
      13  FlickRest                           0x00078b40 -[RKMapperOperation mapRepresentation:atKeyPath:usingMapping:] + 1904
      14  FlickRest                           0x0007b4bd -[RKMapperOperation mapRepresentationOrRepresentations:atKeyPath:usingMapping:] + 829
      15  FlickRest                           0x0007be12 -[RKMapperOperation mapSourceRepresentationWithMappingsDictionary:] + 2210
      16  FlickRest                           0x0007c7db -[RKMapperOperation main] + 1403
      17  Foundation                          0x00ca9a69 -[__NSOperationInternal _start:] + 671
      18  Foundation                          0x00c26798 -[NSOperation start] + 83
      19  FlickRest                           0x000ccb7a -[RKObjectResponseMapperOperation performMappingWithObject:error:] + 1354
      20  FlickRest                           0x000cabb3 -[RKResponseMapperOperation main] + 2371
      21  Foundation                          0x00ca9a69 -[__NSOperationInternal _start:] + 671
      22  Foundation                          0x00c26798 -[NSOperation start] + 83
      23  Foundation                          0x00cabd34 __NSOQSchedule_f + 62
      24  libdispatch.dylib                   0x028de4b0 _dispatch_client_callout + 14
      25  libdispatch.dylib                   0x028cc088 _dispatch_queue_drain + 450
      26  libdispatch.dylib                   0x028cbe85 _dispatch_queue_invoke + 126
      27  libdispatch.dylib                   0x028cce25 _dispatch_root_queue_drain + 83
      28  libdispatch.dylib                   0x028cd13d _dispatch_worker_thread2 + 39
      29  libsystem_c.dylib                   0x02bf6e72 _pthread_wqthread + 441
      30  libsystem_c.dylib                   0x02bdedaa start_wqthread + 30
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  </code></pre>