C# in Depth

LINQ to SQL315LINQ to DataSet and LINQ to XML are both frameworks that tackle existing problems(manipulating datasets and XML respectively) but do so in a LINQ-friendly fashion.Both of them use LINQ to Objects for the underlying query support, but the APIshave been designed so that query expressions can be used to access data in a painlessand consistent manner.Having covered the LINQ APIs shipped with .NET 3.5, we’ll take a peek at someother providers. Microsoft developers aren’t the only ones writing LINQ providers,and I’ll show a few third-party examples, before revealing what Microsoft has in storefor us with the ADO.NET Entity Framework and Parallel LINQ.This chapter is not meant to provide you with a comprehensive knowledge of usingLINQ by any means: it’s a truly massive topic, and I’m only going to scratch the surfaceof each provider here. The purpose of the chapter is to give you a broad idea of whatLINQ is capable of, and how much easier it can make development. Hopefully there’llbe enough of a “wow” factor that you’ll want to study some or all of the providers further.To this end, there are great online resources, particularly blog posts from the variousLINQ teams (see this book’s website for a list of links), but I also thoroughlyrecommend LINQ in Action (Manning 2008).As well as understanding LINQ itself, by the end of this chapter you should see howthe different pieces of the C# 3 feature set all fit together, and why they’re all presentin the first place. Just as a reminder, you shouldn’t expect to see any new features of C#at this point—we’ve covered them all in the previous chapters—but they may wellmake more sense when you see how they help to provide unified querying over multipledata sources.The change in pace, from the detail of the previous chapters to the sprint throughfeatures in this one, may be slightly alarming at first. Just relax and enjoy the ride,remembering that the big picture is the important thing here. There won’t be a testafterward, I promise. There’s a lot to cover, so let’s get cracking with the most impressiveLINQ provider in .NET 3.5: LINQ to SQL.12.1 LINQ to SQLI’m sure by now you’ve absorbed the message that LINQ to SQL converts query expressionsinto SQL, which is then executed on the database. There’s more to it than that,however—it’s a full ORM solution. In this section we’ll move our defect system into aSQL Server 2005 database, populate it with the sample defects, query it, and update it.We won’t look at the details of how the queries are converted into SQL until the nextsection, though: it’s easier to understand the mechanics once you’ve seen the endresult. Let’s start off by getting our database and entities up and running.12.1.1 Creating the defect database and entitiesTo use LINQ to SQL, you need a database (obviously) and some classes representingthe entities. The classes have metadata associated with them to tell LINQ to SQL howthey map to database tables. This metadata can be built directly into the classes usingLicensed to Rhona Hadida