C # Entity Framework using only one ObjectContext for HttpContext

Question

In ASP.NET MVC 2, using Entity Framework 4, I get this error "An entity object cannot reference multiple instances of IEntityChangeTracker."

A SO search shows that, probably because I have different ObjectContext instances of the Entity Framework object, when it should be only one ObjectContext instance for each HttpContext.

I have this code (written long before I joined) that seems to do just that - it has one ObjectContext for each HttpContext. But I often get an "IEntityChangeTracker" exception, so it probably doesn't work as intended:

// in ObjectContextManager.cs public const string ConnectionString = "name=MyAppEntities"; public const string ContainerName = "MyAppEntities"; public static ObjectContext GetObjectContext() { ObjectContext objectContext = GetCurrentObjectContext(); if (objectContext == null) // create and store the object context { objectContext = new ObjectContext(ConnectionString, ContainerName); objectContext.ContextOptions.LazyLoadingEnabled = true; StoreCurrentObjectContext(objectContext); } return objectContext; } private static void StoreCurrentObjectContext(ObjectContext objectContext) { if (HttpContext.Current.Items.Contains("EF.ObjectContext")) HttpContext.Current.Items["EF.ObjectContext"] = objectContext; else HttpContext.Current.Items.Add("EF.ObjectContext", objectContext); } private static ObjectContext GetCurrentObjectContext() { ObjectContext objectContext = null; if (HttpContext.Current.Items.Contains("EF.ObjectContext") objectContext = (ObjectContext)HttpContext.Current.Items["EF.ObjectContext"]; return objectContext; } 

I have studied this code and it looks right. It, as far as I can tell, returns one instance of ObjectContext for each HttpContext. Is the code incorrect?

If the code is not incorrect, why else do I get: "An entity object cannot reference multiple instances of an IEntityChangeTracker exception?

EDIT: show how ObjectContext is placed:

 // in HttpRequestModule.cs private void Application_EndRequest(object source, EventArgs e) { ServiceLocator.Current.GetInstance<IRepositoryContext>().Terminate(); } // in RepositoryContext.cs public void Terminate() { ObjectContextManager.RemoveCurrentObjectContext(); } // in ObjectContextManager.cs public static void RemoveCurrentObjectContext() { ObjectContext objectContext = GetCurrentObjectContext(); if (objectContext != null) { HttpContext.Current.Items.Remove("EF.ObjectContext"); objectContext.Dispose(); } } 

Answer 1

I assume that you saved the object somewhere in memory (most likely, the cache http file using in-process mode, but it can also be any manual cache, such as a common dictionary), and now you somehow linked this object with something else like:

 newOrder.OwnerUser = currentUser; // <== let say currentUser came from cache // and newOrder was on your new entity context 

Therefore, the problem is if the cached object still considers it to be context bound; Last but not least, you probably accidentally save the entire schedule.

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The code looks fine (as long as you delete it at the end of the request), but this would be a good time to add:

 private const string EFContextKey = "EF.ObjectContext"; 

and use this instead of 5 literals. Avoids multiple risks; p