LINQ To SQL Query - Select Customer From Dropdownlist And Then Gridview - Load All Items Of All Orders Of That Customer

I have the following problem: I select a customer from a dropdownlist and then the gridview should load all items of all orders of that customer. I have the following query:

Dim allorders = From ord In db.Orders

Where ord.CustomerID = Convert.ToInt32(CustomerDropDownList.SelectedValue)

[CODE]..............

I also tried to modify the query as follows:

Dim orderitems = From oi In db.OrderItems

Where oi.OrderNumber = (From From ord In db.Orders

[CODE]...........

But this does not work. I just started using LINQ.