Editable WPF ComboBox does not fire PropertyChanged

Question

I have a not editable ComboBox to display all tables of and SQL Database.

 <ComboBox Grid.Column="1" 
                      Grid.Row="2" 
                      Height="23"  
                      Margin="3,3,3,3" Name="cbLogTable" VerticalAlignment="Top"
                      ItemsSource="{Binding}"
                      TextSearch.TextPath="TABLE_NAME"
                      SelectedValue="{Binding Path=LogTable, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, ValidatesOnDataErrors=True}"
                      >
                <ComboBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel>
                            <TextBlock Text="{Binding Path=TABLE_NAME}"/>
                        </StackPanel>

                    </DataTemplate>
                </ComboBox.ItemTemplate>
            </ComboBox>

The property of the containing UserControl looks like this and also implements the INotifyPropertyChanged:

    public string LogTable
    {
        get
        {
            return _logTable;
        }
        set
        {
            if (_logTable == value) return;
            _logTable = value;
            OnPropertyChanged("LogTable");
        }
     }

I use the following data binding to fill the ComboBox:

    private void UpdateLogTable()
    {
        var connection = new SqlConnection(_connectionString);
        connection.Open();
        DataTable t = connection.GetSchema("Tables");
        cbLogTable.DataContext = t;
        connection.Close();
    }

But I don't receive a PropertyChanged notification on changing the selected value of the ComboBox. Where is my fault?

Answer 1

In the binding of SelectedValue:

SelectedValue="{Binding Path=LogTable, 
                        UpdateSourceTrigger=PropertyChanged,
                        Mode=TwoWay,
                        ValidatesOnDataErrors=True,
                        RelativeSource={RelativeSource FindAncestor,
                                        AncestorType={x:Type UserControl}}}"

Otherwise, the binding is looking for LogTable property on the DataTable type (which is the DataContext for the Combobox), and fails silently.