C# Linq to Entities - Reference.EntityKey

Now that I have built a database and here is the corresponding SQL code:


Visual Studio 2008 SP1’s ADO.NET Entity Framework has generated an Entity Model like this:


I have created some methods as follows:

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);







                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.



                catch (Exception ex)





Everything works perfectly except for

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

in the method private void buttonAddPatient_Click(object sender, EventArgs e).

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

Here is my project files.


Could anyone give me some help?

Thank you so much.

What happens is the bed number or roon numbers does no exists?

The bid or rid will be not given the right value; thus, using them will rely on a null reference.

Please test the returned value before using it.

Hope this helps

Hope this helps

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.