public ActionResult List() { var airports = Airports; if (airports == null) { airports = _airportService.GetAirportListInEU(); HttpContext.Response.Headers.Add("from-feed", "true"); Airports = airports; } var countries = airports?.GroupBy(f => f.iso).Select(f => f.Key).OrderBy(f => f).ToList(); var model = new AirportViewModel { Airports = airports, Countries = countries }; return(View(model)); }