Database

private void comboCustomerId_SelectedIndexChanged(object sender, EventArgs e)
{
    ComboBox cb = sender as ComboBox;
    if ((cb != null) && (cb.SelectedValue != null))
    {
        SetDefaultsForCustomer((int)cb.SelectedValue);
    }
}

private void SetDefaultsForCustomer(int customerId)
{
    CustomerDefaultsTableAdapter adap = new CustomerDefaultsTableAdapter();
    InvoiceDataSet.CustomerDefaultsDataTable dfc = adap.GetData(customerId);
    InvoiceDataSet.CustomerDefaultsRow cust = dfc.Rows[0] as InvoiceDataSet.CustomerDefaultsRow;

    DataRowView drv = (DataRowView)bindingSourceHead.Current;
    InvoiceDataSet.InvoiceRow ir = drv.Row as InvoiceDataSet.InvoiceRow;
    if (ir != null)
    {
        ir.CustomerId = cust.CustomerId;
        ir.CustomerContact = cust.ContactPerson;
}

using (DataSet ds = new DataSet())
using (SqlConnection conn = new SqlConnection(connectionString))
using (SqlDataAdapter da = new SqlDataAdapter("select * from TableName", conn))
{
                
    try
    {
        da.Fill(ds);
        ds.ReadXml(@"C:\xmldataset.XML");
        ds.AcceptChanges();
        da.Update(ds);
    }
                [...]