NHibernate TransactionService implemenation example - nhibernate

Question

I keep getting the following message while retrieving my domain objects:
failed to lazily initialize a collection of role no session or session was closed
I know the problem has something to do with lazy loading of the collection on my domain object and i'm trying to fix this, but it would be nice if someone could point me in the right direction. The problem is that i have a using statement on my session object and i would like to get rid of the sessions in my repository classes.
Stefan Steinegger recommended to use a TransactionService wich manages the transactions in the following post:
C# Shared Transactions and NHibernate using IRepository
It would be nice someone can provide a tutorial, example on how to implement such a service.

Answer 1

There's a few different ways that you can handle this within a web application and probably the most common in web applications is a Session Per Web Request.
Inside of Application_Start in global.asax.cs, create the SessionFactory and assign it to a static property:
public static ISessionFactory SessionFactory { get; private set; }
protected void Application_Start(object sender, EventArgs e)
{
// your configuration setup
var configuration = new NHibernate.Cfg.Configuration().Configure();
SessionFactory = configuration.BuildSessionFactory();
}
Then, in Application_BeginRequest in global.asax.cs, open a session using the SessionFactory and bind it to the CurrentSessionContext
protected void Application_BeginRequest(object sender, EventArgs e)
{
var session = SessionFactory.OpenSession();
CurrentSessionContext.Bind(session);
}
and in Application_EndRequest in global.asax.cs, unbind the session and dispose of it
protected void Application_EndRequest(object sender, EventArgs e)
{
var session = CurrentSessionContext.Unbind(SessionFactory);
session.Dispose();
}
Now inside of the application, whenever a session is required, we simply ask the SessionFactory for the current session
public class HomeController : Controller
{
public ActionResult Index()
{
IEnumerable<Product> products = null;
var session = MvcApplication.SessionFactory.GetCurrentSession();
using (var transaction = session.BeginTransaction())
{
// your query, which sounds like it should also eager load
// a child collection
products = session.QueryOver<Product>().List();
transaction.Commit();
}
return View(products);
}
}
There are numerous variations on this, including using a LazySessionContext to lazily create a session only if one is needed for a request, and implementations where ISessionFactory could be injected into you controllers through dependency injection.