public ActionResult TakeConfirmed(int id) { IEnumerable <User> Users = dataOperations.GetUsersTakenBook(id); foreach (User user in Users) { if (user.Us_name == User.Identity.Name) { ModelState.AddModelError("Book_name", "You have already taken this book!"); return(View(dataOperations.Find(id))); } } dataOperations.ChangeQuantity(id); dataOperations.AddTakenBook(id, User.Identity.Name, DateTime.Today); EmailClass mail = new EmailClass(); Book book = dataOperations.Find(id); mail.SendMessage(User.Identity.Name, book.Book_name); return(RedirectToAction("Index")); }