RestKit foreign key relationship mapping not added

Question

I few questions regarding RestKit and foreign key relationship mapping.

Before starting with my questions here is what is in place and working properly.

1. Core Data model

Favorite has the following attributes :

placeIds: transformable type that hold the place ids that are define as user's favorite places.

2. RestKit

a. User data mapping

RKEntityMapping *entityMapping = [RKEntityMapping mappingForEntityForName:[self entityName]
                                                     inManagedObjectStore:[RKManagedObjectStore defaultStore]];

[entityMapping addAttributeMappingsFromDictionary:@{@"id":@"userId"}];
entityMapping.identificationAttributes = @[ @"userId" ];
[entityMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"favorites" toKeyPath:@"favorites" withMapping:[AOFavorite mapping]]];

[entityMapping setAssignsDefaultValueForMissingAttributes:YES];
[entityMapping setAssignsNilForMissingRelationships:YES];

b. Favorite Data mapping

RKEntityMapping *entityMapping = [RKEntityMapping mappingForEntityForName:[self entityName]
                                                     inManagedObjectStore:[RKManagedObjectStore defaultStore]];

[entityMapping addAttributeMappingsFromDictionary:@{@"placeIds":@"placeIds"}];
entityMapping.identificationAttributes = @[ @"userId" ];
[entityMapping addConnection:[AOFavorite placesConnection]];

[entityMapping setAssignsDefaultValueForMissingAttributes:YES];
[entityMapping setAssignsNilForMissingRelationships:YES];

+ (RKConnectionDescription *)placesConnection
{
    NSEntityDescription *entity = [NSEntityDescription entityForName:[self entityName]
                                              inManagedObjectContext:[RKManagedObjectStore defaultStore].mainQueueManagedObjectContext];
    NSRelationshipDescription *places = [entity relationshipsByName][@"places"];
    return [[RKConnectionDescription alloc] initWithRelationship:places attributes:@{ @"placeIds": @"placeId" }];
}

c. Place Data mapping

RKEntityMapping *entityMapping = [RKEntityMapping mappingForEntityForName:[self entityName]
                                                     inManagedObjectStore:[RKManagedObjectStore defaultStore]];

[entityMapping addAttributeMappingsFromDictionary:@{@"id":@"placeId"}];
entityMapping.identificationAttributes = @[ @"placeId" ];

[entityMapping setAssignsDefaultValueForMissingAttributes:YES];
[entityMapping setAssignsNilForMissingRelationships:YES];

User entity has the logged in user object correctly fit into persistent store.

Since the API provide User's favorite places with an array of ids, they are stored into User > Favorite > placeIds

--

I'm using the following method to request the API's object for the Favorite's place relationship with the Route defined as is:

[[[[RKObjectManager sharedManager] router] routeSet] addRoute:[RKRoute routeWithRelationshipName:@"favorite/places"
                                                                                     objectClass:[AOFavorite class]
                                                                                     pathPattern:@"user/favorite/places"
                                                                                          method:RKRequestMethodGET]];

[[RKObjectManager sharedManager] getObjectsAtPathForRelationship:@"favorite/places"
                                                        ofObject:[[AOUser currentUser] favorites]
                                                      parameters:nil
                                                         success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {

                                                         } failure:^(RKObjectRequestOperation *operation, NSError *error) {

                                                         }];

3. Problem and question

a. getObjectsAtPathForRelationship has the places correctly created into the Place entity but the Favorite > Place relationship isn't linked.

b. what is the purpose of having the placeIds into Favorite entities. I have seen SO question/response regarding Foreign key mapping stating that this is the way to do it. Can someone explained why ?