In EF version 1, a reference entity and it’s related EntityReference.EntityKey stay in sync when you change one or the other.

E.g., if you have a sales order, it’s Customer property and the CustomerReference.EntityKey are automatically kept in sync by the ObjectContext.

(Thanks to Craig for poiting out in the comments that I need to clarify an assumption here...the assumptoin is that the Customer entity exists in memory. If it's  not in memory than there is nothing to sync with. )

What happens as we introduce foreign key values into the model? Now we have three pieces of information to synchronize.

Here’s an experiment I did to check what happens.

1. Create a new entity in memory and assign some foreign key properties

 var res=new Reservation();
 res.TripID=34;
 res.ContactID=12;
 res.ReservationDate=DateTime.Now;

2. Add the entity to the context

 context.Reservations.AddObject(res);

3. Then look to see if the EntityReference.EntityKeys were automatically created, and yes they were.

 

4. Next I changed the foreign key value

  res.TripID = 7; 

5. and checked the reference key again.

Again, they were in sync.

6. Changing the EntityKey itself

res.TripReference.EntityKey = 
  new System.Data.EntityKey("BAEntities.Trips", "TripID", 34);

continues to keep the foreign key property in sync.

7. Finally, I queried for an existing trip entity and set my reservation’s Trip navigation property to this trip.

 var trip = context.Trips.First();
 res.Trip = trip;

The TripID of this newly retrieved trip is “1”.

And I can see that the foreign key property and EntityReference.EntityKey continue to stay in sync with this.