Using the entity framework to add existing entities to a collection on a newly created entity

Question

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.

Michael L Perry · Accepted Answer · 2009-12-16 05:16:33Z

5

"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);

answered Dec 16, 2009 at 5:16

Michael L Perry

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2 Comments

Alex James Over a year ago

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: blogs.msdn.com/alexj/archive/2009/06/19/…

Michael L Perry Over a year ago

Brilliant! Yes, what he said.

Craig Stuntz · Accepted Answer · 2009-01-08 01:01:58Z

3

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

order.Contact.Add(contact);

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

edited Jan 8, 2009 at 1:01

answered Jan 5, 2009 at 15:48

Craig Stuntz

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