WPF ComboBox not updating source
I'm trying to get a WPF combobox working (inside the WPFToolkit Datagrid), and I'm having trouble getting all the pieces aligned correctly.  I'm using Linq to Entities, and I'm setting the overall datacontext to  the results of a Linq query:

<pre><code>
private void LoadDonationGrid()
{
	donationGrid.ItemsSource = from donations in entities.Donation
				   .Include("Family")
				   .Include("PledgeYear")
				   .Include("DonationPurpose")
			   from donationPurposes in entities.DonationPurpose
			   select new { donations, donationPurposes };
}
</code></pre>

I also have a page property in my code-behind which provides the ItemsSource for the combobox:

<pre><code>
private IEnumerable<DonationPurpose> donationPurposeList;
public IEnumerable<DonationPurpose> DonationPurposeList
{
	get
	{
		if (donationPurposeList == null)
		{
			donationPurposeList = from dp in entities.DonationPurpose
								  select dp;
		}
		return donationPurposeList.ToList();
	}
}
</code></pre>

The XAML for the combobox looks like this:

    <tk:DataGridTemplateColumn Header="Purpose">
        <tk:DataGridTemplateColumn.CellTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Path=donations.DonationPurpose.Description, Mode=TwoWay}" />
            </DataTemplate>
        </tk:DataGridTemplateColumn.CellTemplate>
        <tk:DataGridTemplateColumn.CellEditingTemplate>
            <DataTemplate>
                <ComboBox Name="cboDonationPurpose"
                    SelectedValue="{Binding Path=donations.DonationPurposeID, Mode=TwoWay}"
                    ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type Page},Mode=FindAncestor},Path=DonationPurposeList}"                                 
                    DisplayMemberPath="Description"
                    SelectedValuePath="DonationPurposeID"
                          />
            </DataTemplate>
        </tk:DataGridTemplateColumn.CellEditingTemplate>
    </tk:DataGridTemplateColumn>

And everything seems to work correctly, i.e., the appropriate values are displayed in the ComboBox, right up to the point where focus leaves the ComboBox.  At that point, the displayed value returns to the original value, not to the newly selected value.  I've tried using SelectedItem instead of SelectedValue, but that ends up with the selected value not showing in the ComboBox.  I'm kinda mystified: it seems like this bit should be working.

Any thoughts?
WPF ComboBox not updating source
===

I'm trying to get a WPF combobox working (inside the WPFToolkit Datagrid), and I'm having trouble getting all the pieces aligned correctly.  I'm using Linq to Entities, and I'm setting the overall datacontext to  the results of a Linq query:

<pre><code>
private void LoadDonationGrid()
{
	donationGrid.ItemsSource = from donations in entities.Donation
				   .Include("Family")
				   .Include("PledgeYear")
				   .Include("DonationPurpose")
			   from donationPurposes in entities.DonationPurpose
			   select new { donations, donationPurposes };
}
</code></pre>

I also have a page property in my code-behind which provides the ItemsSource for the combobox:

<pre><code>
private IEnumerable<DonationPurpose> donationPurposeList;
public IEnumerable<DonationPurpose> DonationPurposeList
{
	get
	{
		if (donationPurposeList == null)
		{
			donationPurposeList = from dp in entities.DonationPurpose
								  select dp;
		}
		return donationPurposeList.ToList();
	}
}
</code></pre>

The XAML for the combobox looks like this:

    <tk:DataGridTemplateColumn Header="Purpose">
        <tk:DataGridTemplateColumn.CellTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Path=donations.DonationPurpose.Description, Mode=TwoWay}" />
            </DataTemplate>
        </tk:DataGridTemplateColumn.CellTemplate>
        <tk:DataGridTemplateColumn.CellEditingTemplate>
            <DataTemplate>
                <ComboBox Name="cboDonationPurpose"
                    SelectedValue="{Binding Path=donations.DonationPurposeID, Mode=TwoWay}"
                    ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type Page},Mode=FindAncestor},Path=DonationPurposeList}"                                 
                    DisplayMemberPath="Description"
                    SelectedValuePath="DonationPurposeID"
                          />
            </DataTemplate>
        </tk:DataGridTemplateColumn.CellEditingTemplate>
    </tk:DataGridTemplateColumn>

And everything seems to work correctly, i.e., the appropriate values are displayed in the ComboBox, right up to the point where focus leaves the ComboBox.  At that point, the displayed value returns to the original value, not to the newly selected value.  I've tried using SelectedItem instead of SelectedValue, but that ends up with the selected value not showing in the ComboBox.  I'm kinda mystified: it seems like this bit should be working.

Any thoughts?