public async Task <IActionResult> Buy(int id) { var value = new byte[0]; if (HttpContext.Session.Keys.Contains("basket")) { value = HttpContext.Session.Get("basket"); } if (!await db.IsAvailable(id)) { return(RedirectToAction("Error", new ErrorViewModel() { ActionName = "Catalog", RequestInfo = "Product not available" })); } HttpContext.Session.Set("basket", value.AddValue(id)); return(RedirectToAction("Basket")); }