Enumeration error on results fetched using nhibernate session create sql query

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

Jay Otterbein Jay Otterbein · Accepted Answer · 2012-03-02T18:54:26

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.

Enumeration error on results fetched using nhibernate session create sql query

1 Answers