Enumeration error on results fetched using nhibernate session create sql query - nhibernate

Question

I am using sharp arch ver 1.0.
In the NHibernate PostUpdateEvent I am trying to access database.
public class PostUpdateListener : IPostUpdateEventListener
{
public void OnPostUpdate(PostUpdateEvent postUpdateEvent)
{
var session = NHibernateSession.Current;
var results = session.CreateSQLQuery("Select * from Storefront").List<object>();
for (int i = 0; i < results.Count; i++)
{
}
}
When I try to save any entity and in the postupdateevent i run this select query, it gives the enumeration error on OnFlush. NHibernate\Listeners\FlushFixEventListener .cs Line: 35
I read that using foreach loop runs enumeration operation so better to run for loop. But I tried with the for loop. still makes no difference.
The save operation is processed with SharArch NHibernate Transaction attribute. If I remove the Transaction attribute the query in the postupdatelistener works fine.
here is the stack trace.
[InvalidOperationException: Collection was modified; enumeration operation may not execute.]
System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) +56
System.Collections.Generic.Enumerator.MoveNextRare() +58
System.Collections.Generic.Enumerator.MoveNext() +93
NHibernate.Engine.ActionQueue.ExecuteActions(IList list) in d:\horn.horn\orm\nhibernate\Working-2.1\src\NHibernate\Engine\ActionQueue.cs:112
NHibernate.Engine.ActionQueue.ExecuteActions() in d:\horn.horn\orm\nhibernate\Working-2.1\src\NHibernate\Engine\ActionQueue.cs:147
NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session) in d:\horn.horn\orm\nhibernate\Working-2.1\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:241
NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) in d:\horn.horn\orm\nhibernate\Working-2.1\src\NHibernate\Event\Default\DefaultFlushEventListener.cs:19
Infrastructure.NHibernate.Listeners.FlushFixEventListener.OnFlush(FlushEvent event) in D:\Solutions\Infrastructure\NHibernate\Listeners\FlushFixEventListener .cs:35
NHibernate.Impl.SessionImpl.Flush() in d:\horn.horn\orm\nhibernate\Working-2.1\src\NHibernate\Impl\SessionImpl.cs:1478
Infrastructure.NHibernate.LinqRepository1.Save(T entity) in D:\Solutions\Infrastructure\NHibernate\LinqRepository.cs:95
Tasks.Shared.ContentEntityTasks4.Save(TSaveEntityRequestDetails details) in D:\Solutions\Tasks\Shared\ContentEntityTasks.cs:96
Web.Controllers.Entity.EntityController.Edit(EntityViewModel entityViewModel, HttpPostedFileBase fileName, HttpPostedFileBase mainImageFileName, HttpPostedFileBase thumbnailFileName) in D:\Solutions\Web.Controllers\Entity\EntityController.cs:379
lambda_method(ExecutionScope , ControllerBase , Object[] ) +185
System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary2 parameters) +236
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) +31
System.Web.Mvc.<>c_DisplayClassa.b_7() +85
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +235491
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +235491
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +235491
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +235491
System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters) +288
System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +235670
System.Web.Mvc.Controller.ExecuteCore() +174
System.Web.Mvc.MvcHandler.ProcessRequest(HttpContextBase httpContext) +209
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +599
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +171

Answer 1

It seems like what is happening is the session is deciding to flush due to the CreateSQLQuery call. That causes the post update event to be added to the list of internal events that need to be fired (guessing at this one).
You should be able to fix it by accessing a child session, instead of the main NH session, by using the event. Like this:
public class PostUpdateListener : IPostUpdateEventListener
{
public void OnPostUpdate(PostUpdateEvent postUpdateEvent)
{
var session = postUpdateEvent.Session.GetSession(EntityMode.Poco)
var results = session.CreateSQLQuery("Select * from Storefront").List<object>();
for (int i = 0; i < results.Count; i++)
{
}
}
}
If you also require adding or updating entities inside this event, for the purposes of an audit log for example, then you'll also want to ensure you flush the inner session.