NHibernate open session in view with HttpModule

brianleebeckham · **Joined:** Mon Jul 17, 2006 3:22 pm **Posts:** 2

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Hibernate version: NHibernate 1.0.2

I am new to NHibernate, but have *some* experience with using Hibernate 3 in Java. As I read the many posts on session management for NHibernate, I began to adopt the HttpModule approach for a "session per request" pattern implementation.

I noticed that in the Java implementation using a filter, a transaction was "started" along with the session obtained. That way, the transaction logic did not have to be embedded within the service layer or within the DAOs themselves.

Here is what I have so far, based on the HttpModule posted by Ed Courtenay:

Code:

public class NHibernateHttpModule : IHttpModule {

        private static readonly string SESSION_KEY = "NHibernateSession";
        private static readonly string TRANSACTION_KEY = "NHibernateTransaction";

        public void Init( HttpApplication context ) {
            context.EndRequest += new EventHandler( context_EndRequest );
        }

        public void Dispose( ) { }

        private void context_BeginRequest( object sender, 
                                           EventArgs e ) {
            HttpApplication application = ( HttpApplication )sender;
            HttpContext context = application.Context;

            ISession session = NHibernateHelper.OpenSession( );
            context.Items[SESSION_KEY] = session;
            ITransaction transaction = session.BeginTransaction( );
            context.Items[ TRANSACTION_KEY ] = transaction;
        }

        private void context_EndRequest( object sender, EventArgs e ) {
            
            HttpApplication application = ( HttpApplication )sender;
            HttpContext context = application.Context;

            ISession session = context.Items[SESSION_KEY] as ISession;
            ITransaction transaction = context.Items[ TRANSACTION_KEY ] as ITransaction;
            
            if ( transaction != null ) {

                try {
                    
                    transaction.Commit( );
                    
                } catch ( Exception ) {
                    
                    transaction.Rollback();
                    throw;
                }

            }
            
            if ( session != null ) {
                try {
                    session.Flush( );
                    session.Close( );
                } catch { }
            }

            context.Items[SESSION_KEY] = null;
            context.Items[TRANSACTION_KEY] = null;
        }

        public static ISession CurrentSession {

            get {

                HttpContext currentContext = HttpContext.Current;
                ISession session = currentContext.Items[SESSION_KEY] as ISession;

                if ( session == null ) {
                    session = NHibernateHelper.OpenSession( );
                    currentContext.Items[SESSION_KEY] = session;
                    ITransaction transaction = session.BeginTransaction( );
                    currentContext.Items[TRANSACTION_KEY] = transaction;
                }

                return session;
            }
        }
        
}

Any idea why this approach would not work?

Code:

`

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

You can find a .NET implementation of this at
http://www.codeproject.com/aspnet/NHibernateBestPractices.asp.
Billy did a similar adaptation of Courtenay's code.

brianleebeckham · **Joined:** Mon Jul 17, 2006 3:22 pm **Posts:** 2

mnichols,

The best practices document you pointed me to really helped - this implementation appears to be very similar to the filter approach from the Java side.

Do you have any personal experience / know of anyone using this approach in .NET? What will the application container do in the event an exception is thrown from the commit in the filter? I am still working on the implemenation so I haven't begun testing as of yet.

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

It depends on the flush mode you are using. Personally, i flushmode.commit so any exceptions occuring in my Repository are wrapped with a more generic PersistenceException and then bubbles on up to the Service Layer for handling.

If you look in Billy's NHibernateSessionManager class, you'll see the transactino being committed and if there are exceptions, the transaction is rolled back and then the exception rethrown, which in turn can be handled by layers higher up (like in a service layer that made the call inside a try...catch block).

This is a very common scenario for ASP.NET apps using NHibernate.

That help?