C# in Depth

Evolution in action: examples of code change15Personally, I find the earlier listing easier to read—the only benefit to the queryexpression version is that the where clause is simpler.So if query expressions are no good, why is everyone making such a fuss aboutthem, and about LINQ in general? The first answer is that while query expressions arenot particularly suitable for simple tasks, they’re very, very good for more complicatedsituations that would be hard to read if written out in the equivalent method calls(and fiendish in C# 1 or 2). Let’s make things just a little harder by introducinganother type—Supplier. I haven’t included the whole code here, but complete readyto-compilecode is provided on the book’s website (www.csharpindepth.com). We’llconcentrate on the fun stuff.Each supplier has a Name (string) and a SupplierID (int). I’ve also addedSupplierID as a property in Product and adapted the sample data appropriately.Admittedly that’s not a very object-oriented way of giving each product a supplier—it’s much closer to how the data would be represented in a database. It makes thisparticular feature easier to demonstrate for now, but we’ll see in chapter 12 thatLINQ allows us to use a more natural model too.Now let’s look at the code (listing 1.15) to join the sample products with the samplesuppliers (obviously based on the supplier ID), apply the same price filter asbefore to the products, sort by supplier name and then product name, and print outthe name of both supplier and product for each match. That was a mouthful (fingerful?)to type, and in earlier versions of C# it would have been a nightmare to implement.In LINQ, it’s almost trivial.Listing 1.15Joining, filtering, ordering, and projectingList products = Product.GetSampleProducts();List suppliers = Supplier.GetSampleSuppliers();var filtered = from p in productsjoin s in 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);}The more astute among you will have noticed that it looks remarkably like SQL. 2Indeed, the reaction of many people on first hearing about LINQ (but before examiningit closely) is to reject it as merely trying to put SQL into the language for the sakeof talking to databases. Fortunately, LINQ has borrowed the syntax and some ideasfrom SQL, but as we’ve seen, you needn’t be anywhere near a database in order to use2If you’ve ever worked with SQL in any form whatsoever but didn’t notice the resemblance, I’m shocked.Licensed to Rhona Hadida