Session variables in action filter

Question

I have an action filter checks whether or not a session variable ID is set. For development purposes, I have manually set this variable prior to the check.

public class MyActionFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(ActionExecutedContext context)
        {

            context.HttpContext.Session.Add("ID", 123123);

            int ID = (int)context.HttpContext.Session.Contents["ID"];
            var rd = context.HttpContext.Request.RequestContext.RouteData;

            TED _db = new TED();

            //if not in DB
            if (_db.Users.Find(ID) == null && rd.GetRequiredString("action") != "NoAccess")
            {
                RouteValueDictionary redirectTargetDictionary = new RouteValueDictionary();
                redirectTargetDictionary.Add("action", "NoAccess");
                redirectTargetDictionary.Add("controller", "Home");
                redirectTargetDictionary.Add("area", "");

                context.Result = new RedirectToRouteResult(redirectTargetDictionary);
            }

            base.OnActionExecuted(context);
        }
    }

As far as I understand, this code is run prior to any page, this Session["ID"] is always set. The site works fine if I am consistently testing, but it seems to break if I leave it for a while then try to continue testing. Here is the error I get:

int UserID = (int)Session.Contents["ID"];
System.NullReferenceException: Object reference not set to an instance of an object.

Initially I thought the session may simply be expiring, but prior to any page loading, Session["ID"] should be getting set. What is the issue here?

Solution

you're implementing your actionfilter's on OnActionExecuted method which executes AFTER your action method

You should implement the OnActionExecuting method

public class MyActionFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext context)
        {

            context.HttpContext.Session.Add("ID", 123123);

            int ID = (int)context.HttpContext.Session.Contents["ID"];
            var rd = context.HttpContext.Request.RequestContext.RouteData;

            TED _db = new TED();

            //if not in DB
            if (_db.Users.Find(ID) == null && rd.GetRequiredString("action") != "NoAccess")
            {
                RouteValueDictionary redirectTargetDictionary = new RouteValueDictionary();
                redirectTargetDictionary.Add("action", "NoAccess");
                redirectTargetDictionary.Add("controller", "Home");
                redirectTargetDictionary.Add("area", "");

                context.Result = new RedirectToRouteResult(redirectTargetDictionary);
            }

            base.OnActionExecuting(context);
        }
    }

Comments

[Jeff]

Doh! It's the smallest things that get you sometimes... Also, I edited your answer to change these lines: public override void OnActionExecuting(ActionExecutedContext context) base.OnActionExecuted(context); To say Executing also

[Dave Alperovich]

always the small things that kill! big ones are easy to find.

[Jim Moriarty]

This code doesn't even compile! The method signature is wrong.

[Dave Alperovich]

@dvallejo, I guess you missed the point of my answer. I didn't really scan OP's code. I simply pointed out the part that I was clearly wrong. I assumed the rest worked. The signature and compilation doesn't have anything to do with OP using the wrong override.

[Mwas]

I am unable to use this approach in .netcore, I am getting Cannot apply indexing with [] to an expression of type iSession . What can I do?

[Dave Alperovich]

@Mwas, this should technically be posted as a new question pertaining to .NET Core, but to answer your question, in Core, the new filter should inherit from the IActionFilter interface