Datagrid inside datagrid

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C#

WPF

I want to show datagrid if row of other datagrid is selected
XAML

<datagrid x:name="Concours" isreadonly="True" autogeneratecolumns="True" canuserreordercolumns="True" canuserresizecolumns="True" canuserresizerows="False" canusersortcolumns="True" selectionchanged="Concour_SelectionChanged" horizontalalignment="Left" margin="288,48,0,0" verticalalignment="Top" height="345" width="652" xmlns:x="#unknown">
            <datagrid.rowdetailstemplate>
                <datatemplate>
                    <datagrid x:name="{Binding Epreuve}" isreadonly="False" canuseraddrows="True" canuserdeleterows="True" canuserreordercolumns="True" canuserresizecolumns="True" canusersortcolumns="True" canuserresizerows="False" rowdetailsvisibilitymode="VisibleWhenSelected">
                        <datagrid.columns>
                            <datagridtextcolumn header="Code" binding="{Binding Code}" />
                            <datagridtextcolumn header="Désignation" binding="{Binding Designation}" />
                            <datagridtextcolumn header="Coefficient" binding="{Binding Coef}" />
                            <datagridtextcolumn header="Date" binding="{Binding Date}" />
                        </datagrid.columns>
                    </datagrid>
                </datatemplate>
            </datagrid.rowdetailstemplate>
        </datagrid>

What I have tried:

XAML
C#

private void Concour_SelectionChanged (object sender, EventArgs e)
{
    //Get the First Cell Value
    DataTable dt = new DataTable();
    dt = ((DataView)Concours.ItemsSource).ToTable();
    List<string> L = new List<string>();
    foreach (DataRow row in dt.Rows)
    {
        L.Add((String)row[0]);
    }
    int row_number = Concours.SelectedIndex;
    //Connect To DataBase (gestion_concour)
    MySqlConnectionStringBuilder builder = new MySqlConnectionStringBuilder();
    builder.Server = "127.0.0.1";
    builder.UserID = "root";
    builder.Password = "root";
    builder.Database = "gestion_concour";
    MySqlConnection connection = new MySqlConnection(builder.ToString());
    connection.Open();
    //Fill Epreuve
    String q = "SELECT * FROM gestion_Concour.concour WHERE Code = @Code";
    MySqlCommand cmd = new MySqlCommand(q, connection);
    cmd.CommandText = q;
    cmd.Parameters.AddWithValue("@Code", L[row_number]);
    cmd.ExecuteNonQuery();
    MySqlDataAdapter DA = new MySqlDataAdapter(cmd);
    DataTable DT = new DataTable("Epreuve");
    DA.Fill(DT);
    Epreuve.ItemSource = DT.DefaultView;
    DA.Update(DT);
    connection.Close();
}

ERROR :The name 'Epreuve' does not exist in the current context