Více hodnot v jednom poli (cizí klíče?)

Jak mě vyhledávají datové třídy Linq 2 SQL:

Kód, který k tomu patří:

//I have 2 columns in my dataGridView, Id 1st amount 2nd
//I added 3 items for testing
List<Tuple<int, int>> cart = new List<Tuple<int,int>>();
foreach (DataGridViewRow row in dataGridView1.Rows)
{
    if (row.Cells[0].Value != null && row.Cells[1].Value != null)
    { 
        cart.Add(new Tuple<int, int>(Convert.ToInt32(row.Cells[0].Value.ToString()),Convert.ToInt32(row.Cells[1].Value.ToString())));
                //Now each list item will have .Item1 (productId) and .Item2 (amount)
    }
}
using (DataClasses1DataContext dataContext = new DataClasses1DataContext())
{
    //The tables you add in the dataContext are accessible by name
    Order order = new Order();
    dataContext.Orders.InsertOnSubmit(order);
    dataContext.SubmitChanges(); // Submit once so we get an orderId
    foreach (Tuple<int, int> product in cart)
    {
        OrderProduct orderProduct = new OrderProduct();
        orderProduct.OrderId = order.OrderID;
        orderProduct.ProductId = product.Item1;
        orderProduct.Amount = product.Item2;
        dataContext.OrderProducts.InsertOnSubmit(orderProduct);
    }
    dataContext.SubmitChanges();
}