         objectManager.addResponseDescriptor(mixtapeDetail)
         
         // Setup Track Mapping
-        let trackMap = RKObjectMapping(forClass: Track.self)
-        
-        let trackAttributeMap = [
+        let trackMapping = RKObjectMapping(forClass: Track.self)
+        trackMapping.addAttributeMappingsFromDictionary([
             "id":             "id",
             "title":            "title",
             "artist":           "artist",

            "ticket_url":       "ticketURL",
            "play_count":       "playCount",
            "order":            "order",
        ]
        
        trackMap.addAttributeMappingsFromDictionary(trackAttributeMap)
        
        let trackList = RKResponseDescriptor(
            mapping: trackMap,
            method: .GET,
            pathPattern: Path.Track.List(),
            keyPath: "results",

        objectManager.addResponseDescriptor(collectionList)
        
        let collectionDetail = RKResponseDescriptor(
            mapping: collectionMapping,
            method: .GET,
            pathPattern: Path.Collection.Detail(),
            keyPath: nil,
            statusCodes: NSIndexSet(index: 200)
        )

        objectManager.addResponseDescriptor(collectionDetail)
        
        // Setup Mixtape Mapping
        let mixtapeMapping = RKObjectMapping(forClass: Mixtape.self)
        mixtapeMapping.addAttributeMappingsFromDictionary([
            "id":                   "id",
            "title":                "title",
            "slug":                 "slug",
