string hqlQuery = "from StaffMember stm "
                + "left join fetch stm.DepartmentPosition dpo "
                + "left join fetch dpo.PositionType ptp "
                + "left join fetch dpo.Department dpt "
                + "left join fetch stm.Professional pro "
                + "left join fetch pro.Person per "
                + "where stm.UserName = :UserName";

            StaffMember staffMember = null;

            try
            {
                ISession session = NHibernateHelper.GetCurrentSession();

                staffMember = (StaffMember)session.CreateQuery(hqlQuery)
                                            .SetString("UserName", userName)
                                            .UniqueResult<StaffMember>();
            }
            catch (HibernateException hEx)
            {
                ExceptionManager.HandleException(this, hEx);
            }
            catch (Exception ex)
            {
                ExceptionManager.HandleException(this, ex);
            }
            finally
            {
                NHibernateHelper.CloseSession();
            }

2. Stack trace:
   at NHibernate.Loader.Loader.DoList(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Loader.Loader.List(ISessionImplementor session, QueryParameters queryParameters, ISet querySpaces, IType[] resultTypes)
   at NHibernate.Hql.Classic.QueryTranslator.List(ISessionImplementor session, QueryParameters queryParameters)
   at NHibernate.Impl.SessionImpl.Find(String query, QueryParameters parameters, IList results)
   at NHibernate.Impl.SessionImpl.Find(String query, QueryParameters parameters)
   at NHibernate.Impl.QueryImpl.List()
   at NHibernate.Impl.AbstractQueryImpl.UniqueResult[T]()
   at KnowledgeTech.Umby.Repository.NHibernateRepositories.StaffMemberRepositoryNHibernate.FindByUserName(String domainAndUserName)


3. NHibernateHelper class:

public class NHibernateHelper
{
        private static readonly ISessionFactory sessionFactory;
        private static ISession _currentSession;

        static NHibernateHelper()
        {
            sessionFactory = new Configuration().Configure().BuildSessionFactory();
        }

        public static ISession GetCurrentSession()
        {
            if (_currentSession == null || !_currentSession.IsOpen)
            {
                _currentSession = sessionFactory.OpenSession();
            }

            return _currentSession;
        }

        public static void CloseSession()
        {
            _currentSession.Close();
        }
}

  <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
    <session-factory>
      <property name="dialect">NHibernate.Dialect.MsSql2005Dialect</property>
      <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
      <property name="connection.connection_string">Data Source=localhost;Initial Catalog=CaseFileMgmtSys;Integrated Security=True</property>
      <mapping assembly="KnowledgeTech.Umby.Domain" />
    </session-factory>
  </hibernate-configuration>

         // the nhibernate session is a singleton to the http request
         HttpContext currentContext = HttpContext.Current;
       
         ISession session = currentContext.Items[KEY_NHIBERNATE_SESSION] as ISession;

         if (session == null)
         {
            session = CreateSession();
            currentContext.Items[KEY_NHIBERNATE_SESSION] = session;
         }

         return session;

public class NHibernateHelper
{
        private static readonly ISessionFactory sessionFactory;

        [ThreadStatic]
        private static ISession _currentSession;

        static NHibernateHelper()
        {
            sessionFactory = new Configuration().Configure().BuildSessionFactory();
        }

        public static ISession GetCurrentSession()
        {
            if (_currentSession == null || !_currentSession.IsOpen)
            {
                _currentSession = sessionFactory.OpenSession();
            }

            return _currentSession;
        }

        public static void CloseSession()
        {
            _currentSession.Close();
        }
}