Introduction to LINQ - Simple XML Parsing

Every programmer has had to parse an XML file. If you're trying to tell me you haven't, then you're lying and you just don't remember it. You probably shouldn't even call yourself a programmer.

If you don't remember the history of reading an XML document, here's the Cliffs Notes version. In the beginning there was line-by-line parsing. It was hard, error prone, and usually sucked. After a little while of this, light started shining onto our
dark corner of the world. .NET introduced the
XmlTextReader class, and things were good - for a while. And then, as if Microsoft heard the prayers of a million programmers,
LINQ was integrated into .NET 3.5 and again, things are good.

It's the anonymous types and methods introduced into .NET 3.5 that makes LINQ possible. If you haven't messed with anonymous types yet, I would highly recommend it. MSDN has some
good documentation.

Let's start out this tutorial by looking at some XML code. I've created a small document that outlines some of the tutorials we've created.

<?xml
version="1.0"
encoding="utf-8"
?>

<Tutorials>

<Tutorial>

<Author>The Reddest</Author>

<Title>

Creating an XP Style WPF Button with Silverlight

</Title>

<Date>2/20/2008</Date>

</Tutorial>

<Tutorial>

<Author>The Fattest</Author>

<Title>

Flex And Yahoo Maps

</Title>

<Date>2/12/2007</Date>

</Tutorial>

<Tutorial>

<Author>The Tallest</Author>

<Title>

WPF Tutorial - Creating A Custom Panel Control

</Title>

<Date>2/18/2008</Date>

</Tutorial>

</Tutorials>

First, we're going to use some simple LINQ syntax to create some anonymous objects with the properties, Author, Title, and Date.

XDocument xmlDoc
= XDocument.Load("TestFile.xml");

var tutorials =
from tutorial in xmlDoc.Descendants("Tutorial")

select
new

{

Author = tutorial.Element("Author").Value,

Title = tutorial.Element("Title").Value,

Date = tutorial.Element("Date").Value,

};

The result of this code will be an IEnumerable collection filled with anonymous objects. What's nice about Visual Studio is that you'll even get dot completion for anonymous types.



Anonymous objects are well and good, but usually I want something a little better defined to pass around my application. Let's look at how to create a

List

of

Tutorial

objects.

public
class Tutorial

{

public string Author
{ get;
set;
}

public string Title
{ get;
set;
}

public DateTime Date
{ get;
set;
}

}

...

List<Tutorial> tutorials
=

(from tutorial
in xmlDoc.Descendants("Tutorial")

select new Tutorial

{

Author = tutorial.Element("Author").Value,

Title = tutorial.Element("Title").Value,

Date = DateTime.Parse(tutorial.Element("Date").Value),

}).ToList<Tutorial>();

At this point, you're probably floored at how quickly I was just able to parse that XML document into my collection - I know I am. Let's look at one simple piece I haven't mentioned yet, the

where

clause. Just like SQL, LINQ has the ability to filter results using the

where

keyword. Let's filter down my collection to only tutorials written by The Tallest (his are always the best anyway).

List<Tutorial> tutorials
=

(from tutorial
in xmlDoc.Descendants("Tutorial")

where tutorial.Element("Author").Value
== "The Tallest"

select new Tutorial

{

Author = tutorial.Element("Author").Value,

Title = tutorial.Element("Title").Value,

Date = DateTime.Parse(tutorial.Element("Date").Value),

}).ToList<Tutorial>();

Now my list of tutorials will only contain those written by The Tallest.