C# in Depth

LINQ to XML341You can nest query expressions and do all kinds of other clever things with them.Listing 12.16 generates an element containing the project information: the notificationsubscriptions for a project are embedded within the project element by using anested query. The results are shown beneath the listing.Listing 12.16Generating projects with nested subscription elementsvar projects = new XElement("projects",from project in SampleData.AllProjectsselect new XElement("project",new XAttribute("name", project.Name),new XAttribute("id", project.ProjectID),from subscription in SampleData.AllSubscriptionswhere subscription.Project == projectselect new XElement("subscription",new XAttribute("email", subscription.EmailAddress))));Console.WriteLine (projects);// OutputThe two queries are highlighted in bold. There are alternative ways of generating thesame output, of course—you could use a single query that groups the subscriptions byproject, for instance. The code in listing 12.16 was just the first way I thought of tacklingthe problem—and in cases where the performance isn’t terribly important itdoesn’t matter that we’ll be running the nested query multiple times. In productioncode you’d want to consider possible performance issues more carefully, of course!I won’t show you all the code to generate all the elements—even with LINQ toXML, it’s quite tedious just because there are so many attributes to set. I’ve placed it allin a single XmlSampleData.GetElement() method that returns a root XElement. We’lluse this method as the starting point for the examples in our final avenue ofinvestigation: querying.12.4.3 Queries in LINQ to XMLYou may well be expecting me to reveal that XElement implements IEnumerable andthat LINQ queries come for free. Well, it’s not quite that simple, because there are soLicensed to Rhona Hadida