public static function connectMongoDB()
 {
     $mongo_server = Flight::get("mongo.server");
     $mongo_username = Flight::get("mongo.username");
     $mongo_password = Flight::get("mongo.password");
     $mongo_database = Flight::get("mongo.database");
     $mongoConnectStr = sprintf("mongodb://%s:%s@%s", $mongo_username, $mongo_password, $mongo_server);
     self::$_mongoClient = new MongoClient($mongoConnectStr);
     $gameDB = self::$_mongoClient->{$mongo_database};
     return $gameDB;
 }