Linq to Entities - Reference EntityKey

Question

Now that I have built a database.

Visual Studio 2008 SP1’s ADO.NET Entity Framework has generated an Entity Model like this: http://img835.imageshack.us/img835/1810/carease15test1ef.png

I have created a method as follow:

    private void buttonAddPatient_Click(object sender, EventArgs e)
    {
        using (carease15test1Entities context = new carease15test1Entities())
        {
            long bnumber = Convert.ToInt32(textBoxToBed.Text);
            long rnumber = Convert.ToInt32(textBoxOfRoom.Text);

            long bid = (from b in context.bed
                        where b.bnumber == bnumber
                        select b.bid).First();

            long rid = (from r in context.room
                        where r.rnumber == rnumber
                        select r.rid).First();

            // Create a new bed, and input its details.
            patient p = new patient();
            p.pname = textBoxPatient.Text;
            p.Bed_bid = bid;
            p.bedReference.EntityKey = new EntityKey("carease15test1Entities.bed", "bid", bid);
            p.Bed_Room_rid = rid;
            p.bed.roomReference.EntityKey = new EntityKey("carease15test1Entities.room", "rid", rid);

            context.AddTopatient(p);
            try
            {
                context.SaveChanges();
            }
            catch (OptimisticConcurrencyException ex)
            {
                // Resolve the concurrency conflict by refreshing the // object context before re-saving changes. 
                context.Refresh(System.Data.Objects.RefreshMode.ClientWins, p);
                // Save changes.
                context.SaveChanges();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }

Everything works perfectly except for

p.bed.roomReference.EntityKey = new EntityKey("carease15test1Entities.room", "rid", rid);

It turns out a NullRefenceException saying “Object reference not set to an instance of an object.”

Here is my project files.

http://www.mediafire.com/?w3rjjbxbxw6wacv

Could anyone give me some help?

Thank you so much.

Answer 1

You should do

p.bedReference.Load()

So that contents of p.bed are loaded.

P.S. If you can upgrade to .NET 4.0 it will be done automatically for you.