public ActionResult ReturnBook(int id, int clientId, DateTime?returnDate)
{
if (returnDate == null)
{
ModelState.AddModelError("returnDate", "Return Date is Required!");
return(View("ReturnBookList", _context.BorowedBookList().ToList()));
}
_context.ReturnBook(id, clientId, returnDate);
_context.SaveChanges();
return(RedirectToAction("ReturnBookList"));
}