NHibernate Session Closed In Global Action Filter

Question

I have the following global action filter:

public class AddWidgetsAttribute : ActionFilterAttribute {
    private ISession _session;
    public ISession Session {
        get {
            if (_session == null)
                _session = DependencyResolver.Current.GetService<ISession>();
            return _session;
        }
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext) {
        filterContext.Controller.ViewBag.Widgets = Session.Query<Widget>().ToList();
    }
}

Here's the code which adds the filter in the Application_Start event:

GlobalFilters.Filters.Add(new AddWidgetsAttribute());

This works fine on the first request but then it throws an error telling me the session is closed. If I change the Session property to the following:

public ISession Session {
    get { return DependencyResolver.Current.GetService<ISession>(); }
}

It works fine but it seems like abit of a hack. Is there a nice way to inject the dependency within global action filters?

I'd appreciate the help. Thanks

Answer 1

There is no problem doing this, but, keep in your mind, if you instance a global filter, it will add a single instance into your application. So, your code check if the _session object is not null and instance it, but, when you close the session you still have the reference on the global filter, because it is a single instance, and worst, the session is closed. So, the next access will get a non null object and closed session.

I would keep the DependencyResolver to give me the instance of the session everytime, because you are controlling it in another level (I want to understand you are doing a session per request).

public ISession Session 
{
   get 
   {
      return DependencyResolver.Current.GetService<ISession>();
   }
}

And the asp.net mvc will get the right instance every request.