title: Using addConnectionForRelationship for an array of IDs
body: <p>I am receiving the following response from my REST Server.</p>
  
  <pre><code>{
      id: 1,
      model_id: 1,
      plant_id: 1,
      users: [
         2,
         9
      ]
  }
  </code></pre>
  
  <p>To which I am trying to map the following model:</p>
  
  <pre><code>@property (nonatomic, retain) Model *model; 
  @property (nonatomic, retain) Plant *plant; 
  @property (nonatomic, retain) NSSet *expertUsers;
  </code></pre>
  
  <p>and "expertUsers" is a set of objects, based of a class called "User".</p>
  
  <p>Now, I am trying to follow the same approach I have used in the past to connect users to objects, without having the full object. I have been using the following solution, and it works great for single objects.</p>
  
  <pre><code>[pictureMapping addConnectionForRelationship:@"lastModifiedBy" connectedBy:@{ @"lastModifiedByID": @"identifier" }];
  </code></pre>
  
  <p>However, how can I replicate the same thing, but this time with an array of IDs?</p>
  
  <p>I would need something like this: </p>
  
  <pre><code>[modelExperts addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"users" toKeyPath:@"expertUsers" withMapping:userMapping **addConnectionForRelationship:@"lastModifiedBy" connectedBy:@{ @"lastModifiedByID": @"identifier" }**]];
  </code></pre>
  
  <p><strong>EDIT #1:</strong></p>
  
  <p>Here is my current Core Data model:</p>
  
  <pre><code>@interface Cell : NSManagedObject
  @property (nonatomic, retain) NSNumber *identifier;
  @property (nonatomic, retain) NSSet *managers; // To Many Users
  @end
  
  
  @interface User : NSManagedObject
  @property (nonatomic, retain) NSNumber *identifier;
  @end
  
  RKEntityMapping *cellMapping = [RKEntityMapping mappingForEntityForName:@"Cell" inManagedObjectStore:managedObjectStore];
  cellMapping.identificationAttributes = @[@"identifier"];
  
  NSEntityDescription *cellManagersEntityDescription = [NSEntityDescription entityForName:@"Cell" inManagedObjectContext:managedObjectStore.persistentStoreManagedObjectContext];
  NSRelationshipDescription *userManagersRelationshipDescription = [cellManagersEntityDescription relationshipsByName][@"managers"]; // To many relationship for the `User` entity
  RKConnectionDescription *cellManagersConnection = [[RKConnectionDescription alloc] initWithRelationship:userManagersRelationshipDescription attributes:@{ @"managers": @"identifier" }];
  [cellMapping addConnection:cellManagersConnection];
  </code></pre>
  
  <p>Here is my Rest JSON answer for Cell:</p>
  
  <pre><code>{
  id: 1,
  managersIDs: [
  2
  ],}
  </code></pre>
  
  <p>However, I keep getting the following:</p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Cannot connect relationship: invalid attributes given for source entity 'Cell': managers'
  *** First throw call stack:
  (
  0   CoreFoundation                      0x03c646f4 __exceptionPreprocess + 180
  1   libobjc.A.dylib                     0x02df38b6 objc_exception_throw + 44
  2   CoreFoundation                      0x03c64558 +[NSException raise:format:arguments:] + 136
  3   Foundation                          0x029d45ee -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 116
  4   Poka                                0x001db61f -[RKConnectionDescription initWithRelationship:attributes:] + 1279
  5   Poka                                0x0000bdf3 -[APIConnector setupMapping] + 12451
  6   Poka                                0x000089ef -[APIConnector init] + 159
  7   Poka                                0x001863da -[IJContext createClassInstanceFromRegistration:withProperties:] + 186
  8   Poka                                0x00184f12 -[IJContext instantiateClass:withProperties:] + 594
  9   Poka                                0x00186de0 +[NSObject(Injective) injectiveInstantiate] + 96
  10  Poka                                0x00008275 -[PokaAppDelegate application:didFinishLaunchingWithOptions:] + 309
  11  UIKit                               0x01b65525 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 309
  12  UIKit                               0x01b65d65 -[UIApplication _callInitializationDelegatesForURL:payload:suspended:] + 1536
  13  UIKit                               0x01b6a578 -[UIApplication _runWithURL:payload:launchOrientation:statusBarStyle:statusBarHidden:] + 824
  14  UIKit                               0x01b7e57c -[UIApplication handleEvent:withNewEvent:] + 3447
  15  UIKit                               0x01b7eae9 -[UIApplication sendEvent:] + 85
  16  UIKit                               0x01b6c1f5 _UIApplicationHandleEvent + 736
  17  GraphicsServices                    0x048bc33b _PurpleEventCallback + 776
  18  GraphicsServices                    0x048bbe46 PurpleEventCallback + 46
  19  CoreFoundation                      0x03bdfe95 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53
  20  CoreFoundation                      0x03bdfbcb __CFRunLoopDoSource1 + 523
  21  CoreFoundation                      0x03c0a8ac __CFRunLoopRun + 2156
  22  CoreFoundation                      0x03c09bf3 CFRunLoopRunSpecific + 467
  23  CoreFoundation                      0x03c09a0b CFRunLoopRunInMode + 123
  24  UIKit                               0x01b69cad -[UIApplication _run] + 840
  25  UIKit                               0x01b6bf0b UIApplicationMain + 1225
  26  Poka                                0x0000810d main + 141
  27  libdyld.dylib                       0x032db725 start + 0
  )
  libc++abi.dylib: terminating with uncaught exception of type NSException
  </code></pre>