Using Entity Framework to copy entities between databases

Question

Having 2 separate databases with the same schema, I need to copy entities (records) from one database to another using Entity Framework 4.

I'm creating 2 Contexts, but I'm getting the following error when I add one entity to the second Context:

An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

I know I can avoid that error if i use the Detach method, but in that case the related entities are lost!

Sample code:

        var cx = new MyEntities();

        //eager load related tables
        var allEntities = from x in cx.Reservation.Include("Detail.MoreDetail")
                  select x;

        // new instance of context but connected to a second database
        var cx2 = new MyEntities( new ConnectionString...);
        foreach (var e in allEntities)
        {
            //cx.Detach(reservation);  // can't detach, or related entities will be lost
            cx2.AddToReservation(reservation);  // error happens here!
            cx2.SaveChanges();                
        }

How can I perform such operation? Alternatively, how can I detach the entity without losing the related entities?

Answer 1

For once the error message is helpful - entities can only belong to one context at a time. To do what you're wanting you'll need to Detatch each entity from the first context before adding it to the second.

Like you said, this will kill related entities. Unfortunately you'll have to deal with this (annoying) aspect of Detach.