public ActionResult EditPartial(PartialGradesViewModel gradesViewModel)
        {
            if (!ModelState.IsValid)
            {
                ViewBag.Type = "edit";

                string errorString = "";

                foreach (ModelState modelState in ViewData.ModelState.Values)
                {
                    foreach (ModelError error in modelState.Errors)
                    {
                        errorString += error.ErrorMessage + "\n";
                    }
                }
                TempData["Status"] = "invalid";
                TempData["Msg"]    = errorString;

                return(RedirectToAction("EditPartial", new { id = gradesViewModel.grade.id_grade }));
            }

            try
            {
                partialGradesService.Edit(gradesViewModel.grade);
                TempData["Status"] = "success";
                TempData["Msg"]    = "Aktualizacja oceny przebiegła pomyślnie!";
            }
            catch (Exception e)
            {
                TempData["Status"] = "invalid";
                TempData["Msg"]    = "Nie udało się zaktualizować oceny!";
            }
            return(RedirectToAction("List"));
        }