Get datatable from datagrid itemsource without any rowfilter

Hi, I have a datagrid with itemssource set to a datatable in call f1(), later in f2() the datagrid view is changed. Now in call f3() i want to get the entire datatable that was used as itemssource for the datagrid, but the following code only gives me the records after the filter in f(2)

DataGrid dg;
private void f1()
{
    DataTable dt = //some code
    dg.ItemsSource = dt.DefaultView;
}

private void f2()
{
    DataView dv = dgObjects.ItemsSource as DataView;
    if (dv == null) return;

    dv.RowFilter = "WHERE colA = '123'";
}

private void f3()
{
    DataTable dt = ((DataView)dg.ItemsSource).ToTable();
}

How can I retrieve the entire datatable initially used for the datagrid?

Thanks

sri