BindingNavigator with multiple tables updating problem in Visual Studio 2010

I have 2 tables 'contract' and 'customer', they have fk relationship. I drag 'contact' onto form then do so with 'customer', both are details type. The data of 2 tables are sh开发者_如何学Cown on form accordingly. The problem is when I modify then click save button only data of 'contract' table is updated.

 private void button67_Click(object sender, EventArgs e)
    {

        if (textBox81.Text == "")
        {
            MessageBox.Show("you must choose table name");
        }
        if (textBox81.Text != "")
        {
            connect();

            cmd = new OleDbCommand("select  * from  " + textBox81.Text + " ", conn);
            ds = new DataSet();

            dp = new OleDbDataAdapter(cmd);
            dp.Fill(ds,""+textBox81.Text+"");
            cm = (CurrencyManager)this.BindingContext[ds];

            textBox79.DataBindings.Add("text",ds,""+textBox81.Text+""+".ProdS_name");
            textBox80.DataBindings.Add("text", ds, "" + textBox81.Text + "" + ".rate");
        }


    }

private void button58_Click(object sender, EventArgs e)
    {

                       cm.Position++;


    }

    private void button59_Click(object sender, EventArgs e)
    {


            cm.Position= cm.Count - 1; ;


    }

    private void button61_Click(object sender, EventArgs e)
    {

                        cm.Position=0;


    }