How to deal with a non existing session variable?

Question

I am trying to check if a booking record exists, then show its details. Otherwise return to Bookparking page but else part isn't working and shows Object reference not set to an instance of an object because there is no such field with the Session[""]

Controller:

public ActionResult Viewparking()
{
   if (IsUserLoggedIn(Session, Request) == false)
   {
       return RedirectToAction("login");
   }
   else
   {
       String id = Session["username"].ToString();
       ViewBag.userid = id;
       var checkbooking = db.tb_booking.Where(s => s.username == id).FirstOrDefault();
       if (checkbooking != null)
       {
           var show = db.tb_booking.Where(e => e.username == id).FirstOrDefault();
       }
       else
       {   //ViewBag.f = "You have no booking yet!!";
           return RedirectToAction("Bookparking", "user");
       }
       return View();
   }
}

check first `Session["username"]` if it has value, you cannot `.ToString()` null objects and I believe that is the reason of error — Gabriel Llorico, Nov 20 '19 at 07:07
Possible duplicate of [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — Stefan, Nov 20 '19 at 07:40

RoelA · Accepted Answer · 2019-11-20T07:36:51.563

As Gabriel noted, you have not null checked the value from the session. Code would be something like this:

public ActionResult Viewparking()
{
    if (IsUserLoggedIn(Session, Request) == false)
    {
        return RedirectToAction("login");
    }
    else
    {
        String id = Session["username"]?.ToString();
        if (id != null)
        {
            ViewBag.userid = id;
            var checkbooking = db.tb_booking.FirstOrDefault(s => s.username == id);
            if (checkbooking != null)
            {   // TODO: checkbooking is currently unused, except to check if you can fetch it.
                return View();
            }
        }
        // If you reach this code, then either id is null, or the booking was not found
        return RedirectToAction("Bookparking", "user");
    }
}

Or `string id = (string)Session["username"];` – Hans Keﬆing Nov 20 '19 at 08:30 — Hans Keﬆing, Nov 20 '19 at 08:30

How to deal with a non existing session variable?

1 Answers1