Branislav Abadjimarinov's technical blog

Entity Framework in its current version (.net 3.5 sp 1) has some problems with multi-tier application architecture. If you need to use different data context instances for getting an object and submitting the changes made to it you'll face some frustration. Typical scenario in n-tier applications is to use one data context for selecting data and another for submitting the changes made. The problem is that once you  attach an object to the new context you'll lose tracking of all changes made to the object.

The solution is to explicitly call the SetModifiedProperty method  to notify the ObjectStateManager of the data context about the changes.  Also you should be aware that the property's state is set with reflection (when you need to specify a method or class name as string usually reflection is involved (-: )

            AdventureWorksLTEntities context = new AdventureWorksLTEntities();
            Product product = context.ProductSet.FirstOrDefault();
            if (product != null)
            {
                product.ListPrice += 10; // product.EntityState is set to Modified
            }

            AdventureWorksLTEntities newContext = new AdventureWorksLTEntities();

            context.Detach(product); // product.EntityState is set to Detached
            newContext.Attach(product);  // product.EntityState is set to Unchanged

            ObjectStateEntry state = newContext.ObjectStateManager.GetObjectStateEntry(product);
            state.SetModifiedProperty("ListPrice"); // product.EntityState is set to Modified

            newContext.SaveChanges();


P.S. Special thanks for this post to the ADO.NET team from Microinvest for introducing this problem to me.