C# in Depth

LINQ to XML343need the string form, and the code becomes hard to format sensibly within the strictlimits of the printed page.Listing 12.17 isn’t doing anything particularly impressive, of course. In particular,it would be easy to achieve a similar effect with a single XPath expression. Joins, however,are harder to express in XPath. They work, but they’re somewhat messy. WithLINQ to XML, we can use our familiar query expression syntax. Listing 12.18 demonstratesthis, showing each open defect’s ID with its assignee and project.Listing 12.18Two joins and a filter within a LINQ to XML queryXElement root = XmlSampleData.GetElement();var query = from defect in root.Descendants("defect")join user in root.Descendants("user")on (int?)defect.Attribute("assigned-to") equals(int)user.Attribute("id")join project in root.Descendants("project")on (int)defect.Attribute("project") equals(int)project.Attribute("id")where (string)defect.Attribute("status") != "Closed"select new { ID=(int)defect.Attribute("id"),Project=(string)project.Attribute("name"),Assignee=(string)user.Attribute("name") };foreach (var defect in query){Console.WriteLine ("{0}: {1}/{2}",defect.ID,defect.Project,defect.Assignee);}I’m not going to pretend that listing 12.18 is particularly pleasant. It has lots of stringliterals (which could easily be turned into constants) and it’s generally pretty wordy. Onthe other hand, it’s doing quite a lot of work, including coping with the possibility of adefect not being assigned to a user (the int? conversion in the join of defect toassignee). Consider how horrible the corresponding XPath expression would have tobe, or how much manual code you’d have to write to perform the same query in directcode. The other standard query operators are available, too: once you’ve got a querysource, LINQ to XML itself takes a back seat and lets LINQ to Objects do most of thework. We’ll stop there, however—you may have seen enough query expressions to makeyou dizzy by now, and if you want to experiment further it’s easy enough to do so.12.4.4 LINQ to XML summaryLike the other topics in this chapter, we’ve barely scratched the surface of the LINQ toXML API. I haven’t touched the integration with the previous technologies such as DOMand XPath, nor have I given details of the other node types—not even XDocument!Even if I were to go through all of the features, that wouldn’t come close toexplaining all the possible uses of it. Practically everywhere you currently deal withXML, I expect LINQ to XML will make your life easier. To reiterate a cliché, the onlylimit is your imagination.Licensed to Rhona Hadida