Exception "Item has already been added." in MetaModel.Register

Question

My Global.asax contains the below code,

public class Global : System.Web.HttpApplication
    {
        private MetaModel _s_Model = new AdvancedMetaModel();
        public MetaModel s_Model
        {
            get
            {
                return _s_Model;
            }
        }

        private MetaModel _a_Model = new AdvancedMetaModel();
        public MetaModel a_Model
        {
            get
            {
                return _a_Model;
            }
        }

        public void RegisterRoutes(RouteCollection routes)
        {
            Dictionary<Helper.ModelName, MetaModel> registeredRoutes = new Dictionary<Helper.ModelName, MetaModel>();

            if (SQLAppModel.ModelQuery.GetUserType() == Utility.Helper.UserType.ApplicationAdmin
                || SQLAppModel.ModelQuery.GetUserType() == Utility.Helper.UserType.SystemAdmin)
            {
                _a_Model.RegisterContext(typeof(SQLAppModel.aEntities), new ContextConfiguration() { ScaffoldAllTables = true });

                /** Full Permission **/
                routes.Add(new DynamicDataRoute("{table}/ListDetails.aspx")
                {
                    Action = PageAction.List,
                    ViewName = "ListDetails",
                    Model = a_Model
                });

                routes.Add(new DynamicDataRoute("{table}/ListDetails.aspx")
                {
                    Action = PageAction.Details,
                    ViewName = "ListDetails",
                    Model = a_Model
                });

                registeredRoutes.Add(Helper.ModelName.Administration, a_Model);
            }

            string supportedEnvironments = System.Configuration.ConfigurationManager.AppSettings[Helper.SupportedEnvironmentsAppSettingsKey].ToString();

            foreach (string supportedEnvironment in supportedEnvironments.Split(','))
            {

                foreach (var supportedSystem in SQLAppModel.ModelQuery.GetSupportedSystems(supportedEnvironment, true))
                {
                    if (supportedEnvironment.ToUpper() == "ORACLE")
                    {
                        if (supportedSystem.Name.ToUpper() == "ADS")
                        {
                            _s_model.RegisterContext(typeof(OracleAppModel.sEntities), new ContextConfiguration()
                            {
                                ScaffoldAllTables = true
                            });

                            routes.Add(new DynamicDataRoute("{table}/ReadOnlyListDetails.aspx")
                            {
                                Action = PageAction.List,
                                ViewName = "ReadOnlyListDetails",
                                Model = s_model
                            });

                            routes.Add(new DynamicDataRoute("{table}/ReadOnlyListDetails.aspx")
                            {
                                Action = PageAction.Details,
                                ViewName = "ReadOnlyListDetails",
                                Model = s_model
                            });
                            registeredRoutes.Add(Helper.ModelName.ADS, s_model);
                        }
                    }
                }

            HttpContext.Current.Session[Helper.RegisteredRouteListSessionKey] = registeredRoutes;
        }

        void Application_Start(object sender, EventArgs e)
        {

        }

        void Session_Start(object sender, EventArgs e)
        {
            SQLAppModel.ModelQuery.GetApplicationUser();
            RegisterRoutes(RouteTable.Routes);
        }
    }

When I debug my application with ASP.NET development web server for the first time, the application works fine and gives the desired result.

But When I stopped the debugging and started it again, it gives the below exception,

Item has already been added. Key in dictionary: 'APP.SQLAppModel.sEntities' Key being added: 'APP.SQLAppModel.sEntities'

Line that throws this exception is _a_Model.RegisterContext(typeof(SQLAppModel.aEntities), new ContextConfiguration() { ScaffoldAllTables = true });

Complete Stack Trace:

[ArgumentException: Item has already been added. Key in dictionary: 'APP.SQLAppModel.sEntities' Key being added: 'APP.SQLAppModel.sEntities'] System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add) +9352427 System.Collections.Hashtable.Add(Object key, Object value) +11 System.Web.DynamicData.MetaModelManager.AddModel(Type contextType, MetaModel model) +96 System.Web.DynamicData.MetaModel.RegisterContext(DataModelProvider dataModelProvider, ContextConfiguration configuration) +727 System.Web.DynamicData.MetaModel.RegisterContext(Func`1 contextFactory, ContextConfiguration configuration) +390 System.Web.DynamicData.MetaModel.RegisterContext(Type contextType, ContextConfiguration configuration) +88 SAMI.Global.RegisterRoutes(RouteCollection routes) in C:\Anand\SAMI\SAMI\SAMI\Global.asax.cs:42 SAMI.Global.Session_Start(Object sender, EventArgs e) in C:\Anand\SAMI\SAMI\SAMI\Global.asax.cs:137 System.Web.SessionState.SessionStateModule.RaiseOnStart(EventArgs e) +8955827 System.Web.SessionState.SessionStateModule.CompleteAcquireState() +148 System.Web.SessionState.SessionStateModule.BeginAcquireState(Object source, EventArgs e, AsyncCallback cb, Object extraData) +561 System.Web.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +96 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Please let me know how to fix this. I'm having hard time identifying the problem.

Answer 1

The problem is that you're calling RegisterRoutes from Session_Start, so it can get called multiple times. You need to call it from Application_Start instead.