msdn LINQ2SQL add with relation between table

Northwind db1 = new Northwind(…);
// Assume Customer c1 and related Orders o1, o2 are retrieved

// Back on the mid-tier, a new context needs to be used
Northwind db2 = new Northwind(…);

// Create new entities for applying changes
Customer c2 = new Customer();
c2.CustomerID = c.CustomerID;
Order o2 = new Order();
o2.OrderID = ...;

c2.Orders.Add(o2);

// Add other related objects needed for updates

// Set properties needed for optimistic concurrency check
...
// Order o1 to be deleted
Order o1 = new Order();
o1.OrderID = ...;

// Tell LINQ to SQL to track the graph transitively
db2.Customers.Attach(c2);
// Now "replay" all the changes

// Updates
c2.ContactName = ...;
o2.ShipAddress = ...;

// New object for insertion
Order o3 = new Order();
o3.OrderID = ...;
c2.Orders.Add(o3);

// Remove order o1
db2.Orders.Remove(o1);

// DataContext now knows how to do update/insert/delete
db2.SubmitChanges();