DataColumn parentColumn = ds.Tables["scadenziario"].Columns["ev_item_id"];
DataColumn childColumn = ds.Tables["newsletter"].Columns["Items.id"];

DataRelation relAll;
relAll = new DataRelation("scadenziario_newsletter", parentColumn, childColumn, false);

ds.Relations.Add(relAll);

foreach (DataRow custRow in ds.Tables["scadenziario"].Rows)
{
      Console.WriteLine(custRow["ev_id"] + " " + custRow["ev_titolo"]);

       foreach (DataRow orderRow in custRow.GetChildRows(relAll))
            Console.WriteLine(orderRow["Contacts.id"] + " " + orderRow["Company"] + " " + orderRow["Email"]);
}