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:
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.