Hope I'm not bothering you here, but this is a MAJOR hurdle... I'm pulling my hair out over this one!! Spent HOURS today on trying to update the Job.cust_num via pure XAML binding, and I have not accomplished it yet (without using code-behind on SelectionChanged).

Here's a few things I learned (could be wrong on some of this, so please feel free to correct me)

With the Linq-to-Sql modelling and the Association between Job.cust_num and Customer.custno like we are hashing around with here, you CANNOT set the cust_num field of the Job object directly. You get this error in the output window: "A first chance exception of type 'System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException' occurred in wpf2.exe"

And, naturally, the very XAML that I wrote for my UI is causing said error every time I make a selection in the ComboBox, as it is trying set Job.cust_num to the value of the selected item, as the binding instructions have told it to.

          <ComboBox x:Name="dropdownCustomer" IsSynchronizedWithCurrentItem="True" AllowDrop="True"
                    DisplayMemberPath="company" SelectedValuePath="custno"
                    SelectedValue="{Binding Path=cust_num, Mode=TwoWay}"
             />

So, we have already learned that you must change the Customer object within the Job to accomplish what we are after (as far as I have learned from more than one place, this is the way it must be done).

Therefore, I did get it working with the SelectionChanged method and some simple code-behind:

          <ComboBox x:Name="dropdownCustomer" IsSynchronizedWithCurrentItem="True" AllowDrop="True"
                    DisplayMemberPath="company" SelectedValuePath="custno"
                    SelectedValue="{Binding Path=cust_num, Mode=TwoWay}"
                    SelectionChanged="dropdownCustomer_SelectionChanged"                              
            />

Code-behind:

    private void dropdownCustomer_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        ComboBox SendingObject = (ComboBox)sender;

        if (JobToEdit != null) // must check... is null at form launch
            JobToEdit.Customer = (Customer)SendingObject.SelectedItem;
        }
    }

By the way, even though the Customer object is from a totally different source context, this does work! (I had heard that objects that are EXACTLY the same are handled this way by the CLR.)

Only thing I still don't like is: Because of the SelectedItem="{Binding Path=cust_num}" in the XAML (which is necessary to point the ComboBox to the correct Customer at the launching of the form), although you do not get a run-time error, and everything in the app works exactly like I want, BUT, if you look at the Output Window it is giving that stupid "A first chance exception of type 'System.Data.Linq.ForeignKeyReferenceAlreadyHasValueException' occurred in wpf2.exe" error with every selection of the ComboBox. I need to figure out how to synch up without SelectedValue.

I have not found one single example on the internet that addresses this matter thoroughly enough to show what to do. Most examples are based on ad-hoc made-on-the-fly object lists that work good for demo, and they sure make it look easy. Let's see 'em do it against real data from a Linq-to-Sql model.



I did experiment with your suggestion on trying to bind SelectedValue to a Customer reference, but I could not get it wired the right way to make it work.





>>Dude, I hope you read this soon!!
>
>I did. <g>
>
>Your catching up to me I learned about this a few weeks ago. What confuses me is I have changing the ID working fine in one of my classes and I don't know why it is working. <g>
>
>What you found was the next thing to try, but let me propose a slightly different solution.
>
>

><ComboBox ItemsSource="{Binding Path=Customers, ElementName=thisControl, Mode=TwoWay}"
>                       SelectedValue="{Binding Path=Customer, Mode=TwoWay}" >
>      <ComboBox.ItemTemplate>
>        <DataTemplate>
>          <TextBlock Text="{Binding Path=company}"/>
>        </DataTemplate>
>      </ComboBox.ItemTemplate>
></ComboBox>
>

>
>Customers is a list of Customer objects.
>Customer is Job.Customer (The object not the ID)
>company is Customer.company
>
>Since the selected value is the object not the id you should not need the extension to your class.
>
>The one point of uncertainty I have is...
>
>If the Customers list is from a different data context than the Job object... does it work?
>
>(This was a long post and I tried to answer it quickly so hopefully I understood it all correctly.)
>
>John
>
>