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This is a simple ActionFilter we can apply to controls that should reuse the same Unit of Work, Identity map etc between repositories used in an action method:

public class UnitOfWorkFilter : IActionFilter
{
    private readonly ISessionContainer _sessionContainer;


    public UnitOfWorkFilter(ISessionContainer sessionContainer)
    {
        Contract.Requires(sessionContainer != null);

        _sessionContainer = sessionContainer;
    }


    public void OnActionExecuted(ActionExecutedContext filterContext)
    {
        _sessionContainer.CloseSession();
    }


    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
        _sessionContainer.OpenSession();
    }
}

Here is the ISessionContainer interface:

public interface ISessionContainer : IDisposable
{
    ISession Session { get; set; }

    void OpenSession();

    void CloseSession();
}

Here is an implementation of the ISessionContainer that will get and store the nHibernate's ISession into the HttpContext:

public class HttpContextSessionContainer : ISessionContainer
{
    private readonly ISessionFactory _sessionFactory;


    public HttpContextSessionContainer(ISessionFactory sessionFactory)
    {
        _sessionFactory = sessionFactory;
    }


    public void Dispose()
    {
        if (Session.IsConnected)
            Session.Close();

        Session.Dispose();

        HttpContext.Current.Items.Remove("NhibSession");
    }


    public ISession Session
    {
        get
        {
            return HttpContext.Current.Items["NhibSession"] as ISession;
        }
        set
        {
            HttpContext.Current.Items.Add("NhibSession", value);
        }
    }


    public void OpenSession()
    {
        Session = _sessionFactory.OpenSession();
    }


    public void CloseSession()
    {
        this.Dispose();
    }
}

Here is an example of a Controller that have dependencies to two Repositories:

Note: This is only an example so you can see how it can be used, so just dummy code

public class AccountController : Controller
{
    public AccountController(IUserRepository users, IRolesRepository roles)
    {
        Contract.Requires(users != null);
        Contract.Requires(roles != null);

        _users = users;
        _roles = roles;
    }


    public ActionResult NewUser(UserPM user)
    {
        _users.Create(...);

        _roles.AddUserToRole(...)

        return View();
    }

    ...
}

Here is an example of the IUserRepository:

public class UserRepository : BaseRepository<User>, IUserRepository
{

    public UserRepository(ISessionContainer sessionContainer) : base(sessionContainer)
    {
    }
}

The BaseRepository has some CRUD methods, the CRUD methods will get the ISession they need through the ISessionContainer's Session property. If the ISessionContainer's Session is empty, the BaseRepository will make a call to the ISessionCintainer's OpenSession to get an open session to work with, but will close the session when the operation is completed.

When the UnitOfWorkFilter is applied to Controllers, the ActionFilter will call the ISessionContainers's OpenSession method and put the ISession into the HTTPContext when an Action method is executing. The Repositories will then reuse the same ISession. When the execution of an Action method is done, the UnitOfWorkFilter's OnActionExecuted will be called and close the session (It will make sure the ISession.Dispose method is called to clear the ISession to avoid memory leaks etc).

There are other ways of sharing ISession between Repositories etc during an request, for example in the Global.asax, let it put the ISession into the HTTPContext and then in the Application_EndRequest dispose it. We can also create a Base Controller to handle it etc. But I wanted to apply an action filter instead to the Controllers that should reuse an ISession. In my current case, it was the best way (at least what I think).

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