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

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

        objectManager.addResponseDescriptor(mixtapeList)
        
        let mixtapeDetail = RKResponseDescriptor(
            mapping: mixtapeMapping,
            method: .GET,
            pathPattern: Path.Mixtape.Detail(),
            keyPath: nil,
