title: Object mapping using Restkit. map array of objects to NSSet
body: <p>I have to map an array to objects. I am using RKObjectMapping. Everything is fine but the Rewards array is not getting mapped. Getting the rewards NSSet  as null. </p>
  
  <p>In <code>@interface VBDealDetail : NSObject</code></p>
  
  <pre><code>@property(nonatomic,retain) NSString *dealName;
  @property(nonatomic,retain) NSNumber *dealID;
  @property(nonatomic,retain) NSSet *rewards;
  </code></pre>
  
  <p>In my controller class...</p>
  
  <pre><code>RKObjectManager *manager                  = [[VBRestKit sharedDataManager] objectManager];    
  RKObjectMapping *dealDetailEntryMapping   = [RKObjectMapping mappingForClass:[VBDealDetailEntries class]];    
  RKObjectMapping *successResponseMapping   = [RKObjectMapping mappingForClass:[VBCommonResponse class]];
  [successResponseMapping addAttributeMappingsFromDictionary:@{
   @"code":  @"code",
   @"msg" :  @"message"
   }];
  
  RKObjectMapping* rewardMapping  = [RKObjectMapping mappingForClass:[VBRewards class] ];
  // NOTE: When your source and destination key paths are symmetrical, you can use addAttributesFromArray: as a shortcut instead of addAttributesFromDictionary:
  [rewardMapping addAttributeMappingsFromDictionary:@{@"rewardId":@"rewardID",
                                                      @"rewardTitle":@"rewardTitle" }];
  RKObjectMapping *dealDetailMapping        = [RKObjectMapping mappingForClass:[VBDealDetail class]];
  
  [dealDetailMapping addAttributeMappingsFromDictionary:@{
  
   @"dealId"                               : @"dealID",
   @"dealName"                             : @"dealName"
   }];
  [dealDetailEntryMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:  @"response"
                                                                                         toKeyPath:  @"commonResponse"
                                                                                       withMapping:  successResponseMapping]];
  
  [dealDetailEntryMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:  @"dealDetails"
                                                                                         toKeyPath:  @"dealDetail"
                                                                                       withMapping:  dealDetailMapping]];
  
  [dealDetailEntryMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"reward"
                                                                                         toKeyPath:@"rewards"
                                                                                       withMapping:rewardMapping]];
  
  RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:   dealDetailEntryMapping
                                                                                     pathPattern:   nil
                                                                                         keyPath:   @"dealCollection"
                                                                                     statusCodes:   RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
  [manager addResponseDescriptor:responseDescriptor];
  </code></pre>