title: RestKit Core Data mapping connection with foreign key in the URL
body: <p>I have an API with two endpoints:</p>
  
  <p><strong>/projects</strong></p>
  
  <pre><code>{
    project_list:[{"project_id": 1, "project_name": "Ben"},
                  {"project_id": 2, "project_name": "Jerry"}]
  }
  </code></pre>
  
  <p><strong>/projects/1/members</strong></p>
  
  <pre><code>{
    member_list:[{"member_id": 1, "member_name": "Ben"},
                 {"member_id": 2, "member_name": "Jerry"}]
  }
  </code></pre>
  
  <p>A project has-many members and a member has-one project. I'm using RestKit 0.20.1 to map these to a Core Data store.</p>
  
  <p><em>Current code:</em></p>
  
  <pre><code>// ###############################
  // ## Configure Project mapping ##
  // ###############################
  RKEntityMapping *projectMapping = [RKEntityMapping mappingForEntityForName:@"Project" inManagedObjectStore:managedObjectStore];
  projectMapping.identificationAttributes = @[ @"projectId" ];
  [projectMapping addAttributeMappingsFromDictionary:@{ @"project_id": @"projectId",
                                                      @"project_name": @"projectName"}];
  
  RKResponseDescriptor *projectDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:projectMapping pathPattern:nil keyPath:@"project_list" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
  [manager addResponseDescriptorsFromArray:@[ projectDescriptor ]];
  
  // ##############################
  // ## Configure Member mapping ##
  // ##############################
  RKEntityMapping *memberMapping = [RKEntityMapping mappingForEntityForName:@"Member" inManagedObjectStore:managedObjectStore];
  memberMapping.identificationAttributes = @[ @"memberId" ];
  [memberMapping addAttributeMappingsFromDictionary:@{ @"member_id": @"memberId",
                                                     @"member_name": @"memberName"}];
  
  RKResponseDescriptor *memberDescriptior = [RKResponseDescriptor responseDescriptorWithMapping:memberMapping pathPattern:nil keyPath:@"member_list" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
  [manager addResponseDescriptorsFromArray:@[ memberDescriptor ]];
  </code></pre>
  
  <p>The closest I've come are these examples: <a href="http://restkit.org/api/latest/Classes/RKConnectionDescription.html" rel="nofollow">http://restkit.org/api/latest/Classes/RKConnectionDescription.html</a>, but they depend on the foreign key being in the JSON response.</p>
  
  <p><strong>How do I connect these when the project foreign key is in the URL and not returned in the JSON data when retrieving the members?</strong></p>