public IActionResult Upsert(BulkyBook.Models.CoverType cover)
 {
     if (ModelState.IsValid)
     {
         if (cover.Id == 0)
         {
             _coverTypeRepository.Add(cover);
         }
         else
         {
             _coverTypeRepository.Update(cover);
         }
         _coverTypeRepository.Commit();
         return(RedirectToAction(nameof(Index))); // action name
     }
     return(View(cover));
 }
 public IActionResult Upsert(int?id)
 {
     BulkyBook.Models.CoverType cover = new BulkyBook.Models.CoverType(); //SOME ERROR with Single class initialization.
     if (id == null)
     {
         // Create
         return(View(cover));
     }
     // Update
     cover = _coverTypeRepository.GetById(id.GetValueOrDefault());
     if (cover == null)
     {
         // Incorrect ID
         return(NotFound());
     }
     return(View(cover));
 }