How to check if session value is null or session key does not exist in asp.net mvc - 5

Question

I have one ASP.Net MVC - 5 application and I want to check if the session value is null before accessing it. But I am not able to do so.

//Set
System.Web.HttpContext.Current.Session["TenantSessionId"] = user.SessionID;
// Access
int TenantSessionId = (int)System.Web.HttpContext.Current.Session["TenantSessionId"];

I tried many solutions from SO

Attempt

if (!string.IsNullOrEmpty(Session["TenantSessionId"] as string))
 {
                //The code
 }

Kindly guide me.

Error: NULL Reference

Try `if (Session["TenantSessionId"] == null)` or `!=` – Roman Jan 25 '17 at 15:34 — Roman, Jan 25 '17 at 15:34
@Roma : Thank you. You rock! – Unbreakable Jan 25 '17 at 15:40 — Unbreakable, Jan 25 '17 at 15:40

score 27 · Accepted Answer · answered Jan 25 '17 at 15:35

27

if(Session["TenantSessionId"] != null)
{
  // cast it and use it
  // The code
}

answered Jan 25 '17 at 15:35

Ahmed

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Do I need to check bare `session` null too. Please guide me. – Unbreakable Jan 25 '17 at 15:49
I don't see that useful – Ahmed Jan 25 '17 at 15:55

score 7 · Answer 2 · answered Jan 25 '17 at 15:50

7

The NullReferenceException comes from trying to cast a null value. In general, you're usually better off using as instead of a direct cast:

var tenantSessionId = Session["TenantSessionId"] as int?;

That will never raise an exception. The value of tenantSessionId will simply be null if the session variable is not set. If you have a default value, you can use the null coalesce operator to ensure there's always some value:

var tenantSessionId = Session["TenantSessionId"] as int? ?? defaultValue;

Then, it will either be the value from the session or the default value, i.e. never null.

You can also just check if the session variable is null directly:

if (Session["TenantSessionId"] != null)
{
    // do something with session variable
}

However, you would need to confine all your work with the session variable to be inside this conditional.

answered Jan 25 '17 at 15:50

Chris Pratt

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I was using `as` but I was getting some error one of the famous guy in SO "Steve Muecke" told me that better to do classical typecasting. because integer is not reference type and all of that. P.S: I did not use "int ?" I had just `int` in the end – Unbreakable Jan 25 '17 at 15:54
LINK http://stackoverflow.com/questions/41839234/how-to-access-session-variable-in-asp-net-mvc/41839632#41839632 – Unbreakable Jan 25 '17 at 15:57
Yeah, you can't use `as` with a non-nullable, since it returns `null` rather than raising an exception if the value can't be cast. However, if you null coalesce, you can still store in a non-nullable. – Chris Pratt Jan 25 '17 at 16:01

score 6 · Answer 3 · edited Jun 17 '21 at 13:10

6

[] acts as an indexer (like a method on the class) and in this case, session is null and you cannot perform indexing on it.

Try this..

if(Session != null && Session["TenantSessionId"] != null)
{
   // code
}

edited Jun 17 '21 at 13:10

Wai Ha Lee

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answered Jan 25 '17 at 15:40

Rahul Hendawe

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checking this `Session["TenantSessionId"] != null` works for me. Do I need to check for bare `session too`? – Unbreakable Jan 25 '17 at 15:49
1

yes, as I mentioned `[]` this will act as `indexer` and so, sometime it happens when value in a `session` variable is null then it will might throw an error of `null reference`. – Rahul Hendawe Jan 25 '17 at 15:53
I got "The name 'Session' does not exist in the current context", do I need to add any namespaces here? I did a ctrl + dot(.), but there is no fix for it. – paraJdox1 Dec 13 '21 at 06:35

score 1 · Answer 4 · edited Oct 30 '19 at 04:58

1

Check if the session is empty/Null or not in C# MVC Version Lower than 5.

if (!string.IsNullOrEmpty(Session["TenantSessionId"] as string))
{
    //cast it and use it
    //business logic
}

Check if the session is empty/Null or not in C# MVC Version Above 5.

if(Session["TenantSessionId"] != null)
{
    //cast it and use it
    //business logic
}

edited Oct 30 '19 at 04:58

Pergin Sheni

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answered Jul 24 '19 at 09:56

vishpatel73

317
4
10

score 0 · Answer 5 · answered May 21 '21 at 22:02

There is a case when you want to check only for existence of the key itself but not the content. Above method fails when you Session key value is null also.

Eg:

Session["myKey"] = null;
if(Session["myKey"]!=null){}

In above code, I want to check if only the key (not value) exists, I will get false. But the key does exists.

So the only way I could separate this existence check, is by basically checking each key.

static bool check_for_session_key(string SessionKey)
{
     foreach (var key in HttpContext.Current.Session.Keys)
     {
         if (key.ToString() == SessionKey) return true;
     }
     return false;
}
if(check_for_session_key("myKey")){} //checks for the key only

Let me know if you know better way.

Pergin Sheni · Answer 6 · 2019-10-29T12:09:26.753

-1

Check if the session is empty/Null or not

if (!string.IsNullOrEmpty(Session["TenantSessionId"] as string)) {

//here write code for logic

}

edited Oct 29 '19 at 12:09

answered Oct 28 '19 at 11:32

Pergin Sheni

393
2
11

1

Add some Information to your answer, not just code. – tobsob Oct 28 '19 at 11:56

How to check if session value is null or session key does not exist in asp.net mvc - 5

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