C# Linq to Entities - Reference.EntityKey
Now that I have built a database and here is the corresponding SQL code:
http://www.mediafire.com/?f4a0d74j7qe7a1f
Visual Studio 2008 SP1’s ADO.NET Entity Framework has generated an Entity Model like this:
http://postimage.org/image/lulmehljv/
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);
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);
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.
http://www.mediafire.com/?w3rjjbxbxw6wacv
Could anyone give me some help?
Thank you so much.
