Refactoring toward frictionless & odorless code: Getting rid of globals

time to read 5 min | 847 words

Originally posted at 3/30/2011

While I don’t really mind having global state, it tends to bite you on the ass eventually, so let us try to deal with this guy, shall we?

public class NHibernateActionFilter : ActionFilterAttribute
{
    private static readonly ISessionFactory sessionFactory = BuildSessionFactory();

    public static ISession CurrentSession
    {
        get { return HttpContext.Current.Items["NHibernateSession"] as ISession; }
        set { HttpContext.Current.Items["NHibernateSession"] = value; }
    }

    private static ISessionFactory BuildSessionFactory()
    {
        return new Configuration()
            .Configure()
            .BuildSessionFactory();
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        CurrentSession = sessionFactory.OpenSession();
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {

        var session = CurrentSession;
        if (session != null)
        {
            session.Dispose();
        }
    }
}

One easy way to do so would be to put the session directly where we want it to be, in the controller. We already have an extension point for that, the SessionController. Instead of referencing the global session, it can just hold its own:

public class SessionController : Controller
{
    public HttpSessionStateBase HttpSession
    {
        get { return base.Session; }
    }

    public new ISession Session { get; set; }
}

Which leads us to:

public class NHibernateActionFilter : ActionFilterAttribute
{
    private static readonly ISessionFactory sessionFactory = BuildSessionFactory();

    private static ISessionFactory BuildSessionFactory()
    {
        return new Configuration()
            .Configure()
            .BuildSessionFactory();
    }

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        var sessionController = filterContext.Controller as SessionController;

        if (sessionController == null)
            return;

        sessionController.Session = sessionFactory.OpenSession();
    }

    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        var sessionController = filterContext.Controller as SessionController;

        if (sessionController == null)
            return;
        
        var session = sessionController.Session;
        if (session == null) 
            return;

        session.Dispose();
    }
}

Now we have absolutely no global state, and yet we have a very easy access to the current session.

There are still a few things missing, can you see them?