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asp.netsessionsession-stateglobal-asax

"HttpContext.Current.Session" vs Global.asax "this.Session"

Recently, while working on some code for an ASP.NET project at work. We needed a tracking util to take basic metrics on user activity (page hit count etc) we would track them in Session, then save the data to DB via Session_End in Global.asax.

I began hacking away, the initial code worked fine, updating the DB on each page load. I wanted to remove this DB hit on each request though and just rely on Session_End to store all the data.

All of the tracking code is encapsulated in the Tracker class, including properties that essentially wrap the Session variables.

The problem is that when I executed Tracker.Log() in the Session_End method, the HttpContext.Current.Session in the Tracker code was failing with a NullReferenceException. Now, this makes sense since HttpContext always relates to the current request, and of course in Session_End, there is no request.

I know that Global.asax has a Session property which returns a HttpSessionState that actually seems to work fine (I ended up injecting it in to the tracker)..

But I am curious, how the hell can I get the same reference to the HttpSessionState object used by Global.asax from outside of Global.asax?

Thanks in advance guys, I appreciate the input. :)

Solution

  • Global.asax implements HttpApplication - which is what you are talking to when you call this from within it.

    The MSDN documentation for HttpApplication has details on how you can get hold of it in an HttpHandler for example, and then get access to the various properties on it.

    HOWEVER

    Your application can create multiple instances of HttpApplication to handle parallel requests, and these instances can be re-used, so just picking it up somehow isn't going to guarentee that you have the right one.

    I too would also add a note of caution - if your application crashes, there's no guarentee that session_end is going to be called, and you'll have lost all the data across all sessions, clearly not a good thing.

    I agree that logging on every page is probably not a great idea, but perhaps a halfway house with some asynchronous logging happening - you fire details off to a logging class, that every now and then logs the details you are after - still not 100% solid if the app crashes, but you're less likely to lose everything.