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Microsoft Visual Studio 2010: A Beginner’s Guide foreach (var custOrd in customers) { Console.WriteLine( " Name: " + custOrd.Name + " Date: " + custOrd.Date); }
VB: Dim myShop As New MyShopDataContext Dim customers = From cust In myShop.Customers From ord In cust.Orders Select New With { .Name = cust.Name, .Date = ord.OrderDate } For Each custOrd In customers Console.WriteLine( " Name: " & custOrd.Name & " Date: " & custOrd.Date) Next
And here’s the output: Name: Joe Date: 1/5/2010 12:00:00 AM Name: May Date: 10/5/2010 12:00:00 AM Name: May Date: 10/23/2010 12:00:00 AM
Imagine that the preceding code is sitting in the Main method, like what you saw in Listing 7-3. The different part of this query that makes it a select many type of query is the second from clause. Consider the parent/child relationship between Customer and Order, which is represented by cust and ord in this query. The second from clause uses the cust instance to specify the orders to query, which will be all orders belonging to each customer. The ord instance will hold each order belonging to its associated cust. To make this data useful, the projection is on an anonymous type that pulls together the name of the customer and the date of that customer’s order. In the database, I created two orders for May, one order for Joe, and zero orders for Meg. Since there wasn’t an order for Meg, you don’t see any items from Meg in the output. Later, I’ll show you how to add a parent record, even when that parent record has no child records. The select many query is fine for simple queries but becomes harder to use in more complex queries. In this case, a join query emerges as an easier option. Like a select many