C# Linq to Entities - Reference.EntityKey
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Thread: C# Linq to Entities - Reference.EntityKey

  1. #1
    Join Date
    Nov 2011

    C# Linq to Entities - Reference.EntityKey

    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.
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