Object Tracking of EF

The ObjectStateManager is used by the object context to keep track of entities that are loaded into the context.

// Summary:
        //     Occurs when entities are added to or removed from the state manager.
        public event CollectionChangeEventHandler ObjectStateManagerChanged;

If two different queries are done that return the same record from the database, the state manager is aware of that and does not create a new entity. Instead, the same entity is returned.

private static void TrackingDemo()
        {
            using (var data = new Formula1Entities())
            {
                data.ObjectStateManager.ObjectStateManagerChanged += ObjectStateManager_ObjectStateManagerChanged;
                Racer niki1 = data.Racers.Where("it.Country='Austria' && it.Lastname='Lauda'").First();
                Racer niki2 = data.Racers.Where("it.Country='Austria'").
                      OrderBy("it.Wins DESC").First();
                if (Object.ReferenceEquals(niki1, niki2))
                {
                    Console.WriteLine("the same object");
                }
            }

        }

        static void ObjectStateManager_ObjectStateManagerChanged(object sender,
              CollectionChangeEventArgs e)
        {
            Console.WriteLine("Object State change—action: {0}", e.Action);
            Racer r = e.Element as Racer;
            if (r != null)
                Console.WriteLine("Racer {0}", r.Lastname);
        }

The event of the ObjectStateManagerChanged of the ObjectStateManager occurs only once, and the references niki1 and niki2 are indeed the same.