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2132

answers:

2

I am using the Entity framework to create a new order. The order contains a collection of contacts, a many to many relationship. I want to add a reference to an existing contact on the order on creation of the order. Both Order and Contact a Entity Objects.

 Order order = new Order();

 //set details on order

 Contact contact = new Contact();

 EntityKey contactKey =
                    new EntityKey("OrderDetails.Contact",
                        "contact_id", contact.Key.Id);

 contact.EntityKey = contactKey;
 contact.contact_id = contact.Key.Id;

 order.Contact.Attach(contact);  // throws an exception!

 OrderDetails ordTable = new OrderDetails();
            ordTable.AddToOrder(order);
            int result = orgTable.SaveChanges();

When I go to attach, this exception is thrown:

"Attach is not a valid operation when the source object associated with this related end is in an added, deleted, or detached state. Objects loaded using the NoTracking merge option are always detached."

I know I'm probably missing a step or not fully understanding how the entity framework handles many-to-many relationships.

+2  A: 

If Order has a property Contact, then you can do:

order.Contact.Add(contact);

I would suggest making the property called Contact**s** rather than Contact, though.

Craig Stuntz
A: 

"Attach" is not allowed because you haven't saved the order yet. Calling "Add" tells Entity Framework that you want to insert a new contact. So you are left with only one option. You need to load the contact.

Here's the fastest way to do that:

OrderDetails context = new OrderDetails();
Contact contact = context.GetObjectByKey(new EntityKey("OrderDetails.Contact", "contact_id", existingContactId));
order.Contact.Add(contact);
Michael L Perry
Or you can create a stub entity (with the key you know) attach that to the Context (not the collection) and then Add the sub to the collection. See Tip 26 for more: http://blogs.msdn.com/alexj/archive/2009/06/19/tip-26-how-to-avoid-database-queries-using-stub-entities.aspx
Alex James
Brilliant! Yes, what he said.
Michael L Perry