数据在DataGrid中显示两次

Question

我在XAML代码中创建了这样的DataGrid：

<DataGrid x:Name="dgSalons" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Height="100" Width="572" ItemsSource="{Binding}" VerticalScrollBarVisibility="Hidden">
   <DataGrid.Columns>
        <DataGridTextColumn Header="ИД" Binding="{Binding Path = id}" Width="*"/> 
        <DataGridTextColumn Header="Назив" Binding="{Binding Path = name}"  Width="*"/>
        <DataGridTextColumn Header="Адреса" Binding="{Binding Path = adress}" Width="*"/>
        <DataGridTextColumn Header="Телефон" Binding="{Binding Path = email}"  Width="*"/>
        <DataGridTextColumn Header="Интернет адреса" Binding="{Binding Path = web_site}" Width="*"/>
        <DataGridTextColumn Header="ПИБ" Binding="{Binding Path = tin}"  Width="*"/>
        <DataGridTextColumn Header="Матични Број" Binding="{Binding Path = uid}"  Width="*"/>
        <DataGridTextColumn Header="Жиро рачун" Binding="{Binding Path = bank_account}"  Width="*"/>
    </DataGrid.Columns> 
</DataGrid>

我尝试通过单击按钮“显示”（Прикажи）来填充来自mySql的数据：

private void btnShow_Click(object sender, RoutedEventArgs e)
        {
                    string connection = "server=localhost;user id=root; password=root; database=pop-sf40-database";
                    string query = String.Format("SELECT * FROM salons");

                MySqlConnection cn = new MySqlConnection(connection);
                cn.Open();

                MySqlCommand command = new MySqlCommand(query, cn);
                MySqlDataAdapter da = new MySqlDataAdapter(command);

                DataTable data = new DataTable();
                da.Fill(data);
                dgSalons.DataContext = data;
    }

在点击按钮之前，它看起来像这样：

在之后

如何通过绑定仅填充一次细胞？