C# in Depth

Evolution in action: examples of code change17LINQ to SQL know about what to expect in what table, but it’s all fairly straightforward.Listing 1.17 shows the querying code.Listing 1.17Applying a query expression to a SQL databaseusing (LinqDemoDataContext db = new LinqDemoDataContext()){var filtered = from p in db.Productsjoin s in db.Supplierson p.SupplierID equals s.SupplierIDwhere p.Price > 10orderby s.Name, p.Nameselect new{SupplierName = s.Name,ProductName = p.Name};foreach (var v in filtered){Console.WriteLine("Supplier={0}; Product={1}",v.SupplierName, v.ProductName);}}By now, this should be looking incredibly familiar. Everything below the“join” line is cut and pasted directly from listing 1.14 with no changes.That’s impressive enough, but if you’re performance conscious you maybe wondering why we would want to pull down all the data from the databaseand then apply these .NET queries and orderings. Why not get thedatabase to do it? That’s what it’s good at, isn’t it? Well, indeed—andthat’s exactly what LINQ to SQL does. The code in listing 1.17 issues adatabase request, which is basically the query translated into SQL. Eventhough we’ve expressed the query in C# code, it’s been executed as SQL.We’ll see later that the way this query joins isn’t how we’d normally use LINQ to SQL—there’s a more relation-oriented way of approaching it when the schema and the entitiesknow about the relationship between suppliers and products. The result is thesame, however, and it shows just how similar LINQ to Objects (the in-memory LINQoperating on collections) and LINQ to SQL can be.It’s important to understand that LINQ is flexible, too: you can write your ownquery translators. It’s not easy, but it can be well worth it. For instance, here’s an exampleusing Amazon’s web service to query its available books:Query iswritten in C#,but executesas SQLvar query =from book in new LinqToAmazon.AmazonBookSearch()wherebook.Title.Contains("ajax") &&(book.Publisher == "Manning") &&(book.Price