Session variables in ASP.NET MVC

Question

I would think you'll want to think about if things really belong in a session state. This is something I find myself doing every now and then and it's a nice strongly typed approach to the whole thing but you should be careful when putting things in the session context. Not everything should be there just because it belongs to some user.

in global.asax hook the OnSessionStart event

void OnSessionStart(...)
{
    HttpContext.Current.Session.Add("__MySessionObject", new MySessionObject());
}

From anywhere in code where the HttpContext.Current property != null you can retrive that object. I do this with an extension method.

public static MySessionObject GetMySessionObject(this HttpContext current)
{
    return current != null ? (MySessionObject)current.Session["__MySessionObject"] : null;
}

This way you can in code

void OnLoad(...)
{
    var sessionObj = HttpContext.Current.GetMySessionObject();
    // do something with 'sessionObj'
}

The answer here is correct, I however struggled to implement it in an ASP.NET MVC 3 app. I wanted to access a Session object in a controller and couldn't figure out why I kept on getting a "Instance not set to an instance of an Object error". What I noticed is that in a controller when I tried to access the session by doing the following, I kept on getting that error. This is due to the fact that this.HttpContext is part of the Controller object.

this.Session["blah"]
// or
this.HttpContext.Session["blah"]

However, what I wanted was the HttpContext that's part of the System.Web namespace because this is the one the Answer above suggests to use in Global.asax.cs. So I had to explicitly do the following:

System.Web.HttpContext.Current.Session["blah"]

this helped me, not sure if I did anything that isn't M.O. around here, but I hope it helps someone!

Because I dislike seeing "HTTPContext.Current.Session" about the place, I use a singleton pattern to access session variables, it gives you an easy to access strongly typed bag of data.

[Serializable]
public sealed class SessionSingleton
{
    #region Singleton

    private const string SESSION_SINGLETON_NAME = "Singleton_502E69E5-668B-E011-951F-00155DF26207";

    private SessionSingleton()
    {

    }

    public static SessionSingleton Current
    {
        get
        {
            if ( HttpContext.Current.Session[SESSION_SINGLETON_NAME] == null )
            {
                HttpContext.Current.Session[SESSION_SINGLETON_NAME] = new SessionSingleton();
            }

            return HttpContext.Current.Session[SESSION_SINGLETON_NAME] as SessionSingleton;
        }
    }

    #endregion

    public string SessionVariable { get; set; }
    public string SessionVariable2 { get; set; }

    // ...

then you can access your data from anywhere:

SessionSingleton.Current.SessionVariable = "Hello, World!";

If you are using asp.net mvc, here is a simple way to access the session.

From a Controller:

{Controller}.ControllerContext.HttpContext.Session["{name}"]

From a View:

<%=Session["{name}"] %>

This is definitely not the best way to access your session variables, but it is a direct route. So use it with caution (preferably during rapid prototyping), and use a Wrapper/Container and OnSessionStart when it becomes appropriate.

HTH

Well, IMHO..

1. never reference a Session inside your view/master page
2. minimize your useage of Session. MVC provides TempData obj for this, which is basically a Session that lives for a single trip to the server.

With regards to #1, I have a strongly typed Master View which has a property to access whatever the Session object represents....in my instance the stongly typed Master View is generic which gives me some flexibility with regards to strongly typed View Pages

ViewMasterPage<AdminViewModel>

AdminViewModel
{
    SomeImportantObjectThatWasInSession ImportantObject
}

AdminViewModel<TModel> : AdminViewModel where TModel : class
{
   TModel Content
}

and then...

ViewPage<AdminViewModel<U>>

Although I don't know about asp.net mvc, but this is what we should do in a normal .net website. It should work for asp.net mvc also.

YourSessionClass obj=Session["key"] as YourSessionClass;
if(obj==null){
obj=new YourSessionClass();
Session["key"]=obj;
}

You would put this inside a method for easy access. HTH

There are 3 ways to do it.

1. You can directly access HttpContext.Current.Session

2. You can Mock HttpContextBase

3. Create a extension method for HttpContextBase

I prefer 3rd way.This link is good reference.

Get/Set HttpContext Session Methods in BaseController vs Mocking HttpContextBase to create Get/Set methods