Hi All,

I'm currently struggling with this "Collection was modified; enumeration operation may not execute" issue.

I have searched about this error message, and it's all related to the foreach statement. I do have the some foreach statements, but they are just simply representing the data. I did not using any remove or add inside the foreach statement.

NOTE:

1. The error randomly happens (about 4-5 times a day).
2. The application is the MVC website.
3. There are about 5 users operate this applications (about 150 orders a day). Could it be some another users modified the collection, and then occur this error?
4. I have log4net setup and the settings can be found here
5. Make sure that the controller has a parameterless public constructor I do have parameterless public constructor in AdminProductController

Does anyone know why this happen and how to resolve this issue?

A friend (Oskar) mentioned that

"Theory: Maybe the problem is that your configuration and session factory is initialized on the first request after application restart. If a second request comes in before the first request is finished, maybe it will also try to initialize and then triggering this problem somehow."

Many thanks.

Daoming

Here is the error message:

System.InvalidOperationException Collection was modified; enumeration operation may not execute. System.InvalidOperationException: An error occurred when trying to create a controller of type 'WebController.Controllers.Admin.AdminProductController'. Make sure that the controller has a parameterless public constructor. ---> System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> NHibernate.MappingException: Could not configure datastore from input stream DomainModel.Entities.Mappings.OrderProductVariant.hbm.xml ---> System.InvalidOperationException: Collection was modified; enumeration operation may not execute. at System.Collections.ArrayList.ArrayListEnumeratorSimple.MoveNext() at System.Xml.Schema.XmlSchemaSet.AddSchemaToSet(XmlSchema schema) at System.Xml.Schema.XmlSchemaSet.Add(String targetNamespace, XmlSchema schema) at System.Xml.Schema.XmlSchemaSet.Add(XmlSchema schema) at NHibernate.Cfg.Configuration.LoadMappingDocument(XmlReader hbmReader, String name) at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name) --- End of inner exception stack trace --- at NHibernate.Cfg.Configuration.LogAndThrow(Exception exception) at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name) at NHibernate.Cfg.Configuration.AddResource(String path, Assembly assembly) at NHibernate.Cfg.Configuration.AddAssembly(Assembly assembly) at DomainModel.RepositoryBase..ctor() at WebController.Controllers._baseController..ctor() at WebController.Controllers.Admin.AdminProductController..ctor() at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) --- End of inner exception stack trace --- at System.RuntimeType.CreateInstanceImpl(Boolean publicOnly, Boolean skipVisibilityChecks, Boolean fillCache) at System.Activator.CreateInstance(Type type, Boolean nonPublic) at System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) --- End of inner exception stack trace --- at System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) at System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) at System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

UPDATE CODE:

1. In my Global.asax.cs, I'm doing this:

   protected void Application_BeginRequest(object sender, EventArgs e)
   {
       ManagedWebSessionContext.Bind(HttpContext.Current, SessionManager.SessionFactory.OpenSession());
   }
   
   
   protected void Application_EndRequest(object sender, EventArgs e)
   {
       ISession session = ManagedWebSessionContext.Unbind(HttpContext.Current, SessionManager.SessionFactory);
       if (session != null)
       {
           try
           {
               if (session.Transaction != null && session.Transaction.IsActive)
               {
                   session.Transaction.Rollback();
               }
               else
               {
                   session.Flush();
               }
           }
           finally
           {
               session.Close();
           }
       }
   }
   

In the SessionManager class, I'm doing:

public class SessionManager
{
    private readonly ISessionFactory sessionFactory;
    public static ISessionFactory SessionFactory
    {
        get { return Instance.sessionFactory; }
    }

    private ISessionFactory GetSessionFactory()
    {
        return sessionFactory;
    }

    public static SessionManager Instance
    {
        get
        {
            return NestedSessionManager.sessionManager;
        }
    }

    public static ISession OpenSession()
    {
        return Instance.GetSessionFactory().OpenSession();
    }

    public static ISession CurrentSession
    {
        get
        {
            return Instance.GetSessionFactory().GetCurrentSession();
        }
    }

    private SessionManager()
    {

        Configuration config = new Configuration().Configure(); 
        config.AddAssembly(Assembly.GetExecutingAssembly());
        sessionFactory = config.BuildSessionFactory();

    }

    class NestedSessionManager
    {
        internal static readonly SessionManager sessionManager =
            new SessionManager();
    }
}

In the Repository, I'm doing this:

 public IEnumerable<User> GetAll()
    {
        ICriteria criteria = SessionManager.CurrentSession.CreateCriteria(typeof(User));
        return criteria.List<User>();
    }

In the Controller, I'm doing this:

 public class UserController : _baseController
{
    IUserRoleRepository _userRoleRepository;

    internal static readonly ILogger log = LogManager.GetLogger(typeof(UserController));

    public UserController()
    {
        _userRoleRepository = new UserRoleRepository();
    }

    public ActionResult UserList()
    {                    
        var myList = _usersRepository.GetAll();      
        return View(myList);
    }
}