Question

What is the best way to check for the existence of a session variable in ASP.NET C#?

I like to use String.IsNullOrEmpty() works for strings and wondered if there was a similar method for Session. Currently the only way I know of is:

 var session;  if (Session['variable'] != null)  {      session = Session['variable'].ToString();  }  else  {      session = 'set this';      Session['variable'] = session;  } 

Answer 1

To follow on from what others have said. I tend to have two layers:

The core layer. This is within a DLL that is added to nearly all web app projects. In this I have a SessionVars class which does the grunt work for Session state getters/setters. It contains code like the following:

public class SessionVar {     static HttpSessionState Session     {         get         {             if (HttpContext.Current == null)                 throw new ApplicationException('No Http Context, No Session to Get!');              return HttpContext.Current.Session;         }     }      public static T Get<T>(string key)     {         if (Session[key] == null)             return default(T);         else             return (T)Session[key];     }      public static void Set<T>(string key, T value)     {         Session[key] = value;     } } 

Note the generics for getting any type.

I then also add Getters/Setters for specific types, especially string since I often prefer to work with string.Empty rather than null for variables presented to Users.

e.g:

public static string GetString(string key) {     string s = Get<string>(key);     return s == null ? string.Empty : s; }  public static void SetString(string key, string value) {     Set<string>(key, value); } 

And so on…

I then create wrappers to abstract that away and bring it up to the application model. For example, if we have customer details:

public class CustomerInfo {     public string Name     {         get         {             return SessionVar.GetString('CustomerInfo_Name');         }         set         {             SessionVar.SetString('CustomerInfo_Name', value);         }     } } 

You get the idea right? 🙂

NOTE: Just had a thought when adding a comment to the accepted answer. Always ensure objects are serializable when storing them in Session when using a state server. It can be all too easy to try and save an object using the generics when on web farm and it go boom. I deploy on a web farm at work so added checks to my code in the core layer to see if the object is serializable, another benefit of encapsulating the Session Getters and Setters 🙂