public IActionResult DeleteConfirmed(int id)
 {
     try
     {
         _category.Delete(id);
         _book.DeleteBookWithCategoryById(id);
         return(RedirectToAction(nameof(Index)));
     }
     catch (DbUpdateException)
     {
         ModelState.AddModelError("", "Unable to save changes. " +
                                  "Try again, and if the problem persists, " +
                                  "see your system administrator.");
         return(RedirectToAction(nameof(Delete)));
     }
 }