public static void AddRelations(DataSet dataSet)
{
    DataRelation customerOrders = 
        new DataRelation("CustomerOrders",
        dataSet.Tables["Customers"].Columns["customerId"],
        dataSet.Tables["Orders"].Columns["customerId"]);

    DataRelation orderDetails = 
        new DataRelation("OrderDetail",
        dataSet.Tables["Orders"].Columns["orderId"],
        dataSet.Tables["OrderDetails"].Columns["orderId"]);

    dataSet.Relations.AddRange(new DataRelation[] 
        {customerOrders, orderDetails});

    // Display names of all relations.
    foreach (DataRelation relation in dataSet.Relations)
        Console.WriteLine(relation.RelationName.ToString());
}