title: How to use WPF Toolkit Datagrid DataGridTemplateColumn and a combobox?
body: <p>I have a data grid that looks like this</p>
  
  <pre><code>&lt;tk:DataGrid  ItemsSource="{Binding Parents}" AutoGenerateColumns="False"&gt;
                  &lt;tk:DataGrid.Columns&gt;
                  &lt;tk:DataGridTextColumn  Header="Description" Binding="{Binding ID}" /&gt;
  
                  &lt;tk:DataGridTemplateColumn Header="Description" &gt;
                      &lt;tk:DataGridTemplateColumn.CellEditingTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;TextBox Text="{Binding Path=Description, Mode=TwoWay}" /&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/tk:DataGridTemplateColumn.CellEditingTemplate&gt;
                      &lt;tk:DataGridTemplateColumn.CellTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;TextBlock Text="{Binding Path=Description}"/&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/tk:DataGridTemplateColumn.CellTemplate&gt;
                  &lt;/tk:DataGridTemplateColumn&gt;
  
                  &lt;tk:DataGridTemplateColumn Header="Child Description" &gt;
                      &lt;tk:DataGridTemplateColumn.CellEditingTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;ComboBox  SelectedIndex="{Binding Path=ChildID}"  ItemsSource="{Binding Path=Children}" /&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/tk:DataGridTemplateColumn.CellEditingTemplate&gt;
                      &lt;tk:DataGridTemplateColumn.CellTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;TextBlock Text="{Binding Path=Children.Description}"/&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/tk:DataGridTemplateColumn.CellTemplate&gt;
                  &lt;/tk:DataGridTemplateColumn&gt;
              &lt;/tk:DataGrid.Columns&gt;
          &lt;/tk:DataGrid&gt;
  </code></pre>
  
  <p>The view is bound to a ViewModel that exposes a list of Parents which should be my rows and a Children list which is supposed to be the combobox dropdown contents.  The way it is set up I get my rows of Parents, but no data in the Child Description column.  When I double click the row becomes editable and the combobox shows up.  But no data.  When I look in the output window I see the binding error Saying  "BindingExpression path error: 'Children' property not found on 'object' ''Parent' ".  I know...How do I tell it to look up one level?  I've tried binding the datagrid to just the viewmodel, but then no rows show up.  I've tried using the relativesource markup and I still can't get it to see what I want it to see.  I'm sure my syntax is incorrect.  And I could not find any examples.  What am I doing wrong?</p>