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Editorial Team
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Asked: 2026-06-11T03:28:30+00:00

I expect that if controller has attribute SessionStateBehavior.ReadOnly then I can’t change session variables

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I expect that if controller has attribute SessionStateBehavior.ReadOnly then I can’t change session variables inside this controller
but I can change values.

I try this code

 [SessionState(System.Web.SessionState.SessionStateBehavior.ReadOnly)]
    public class GLobalController : Controller
    {
      public  ActionResult Index()
        {
            Session["xxx"] = DateTime.Now.ToString();
            return View();
        }
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1 Answer

  1. Editorial Team

    see Writing to a read only session in MVC 3+

    That post claims the behavior is inconsistent.
    I am definitely able to write to Session in Controllers using ReadOnly.

    I Would treat it like this:

  2. Required means you are requesting a exclusive lock on Session (i.e. no parallel processing of requests for the same sessionID)
  3. ReadOnly means you are requesting a non-exclusive lock on Session (i.e. your request still has to wait for requests with an exclusive lock to finish, but you can process requests with non-exclusive locks in parallel. However it is up to you to ensure that your code doesn’t write to Session. It’s not necessarily enforced by the framework)

    4. I realize this is counter to http://msdn.microsoft.com/en-us/library/system.web.sessionstate.sessionstatebehavior.aspx

    Read-only session state is enabled for the request. This means that session state cannot be updated.

    but it seems you in fact can update session state under some scenarios.

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