Multiple namespaces when using LINQ to XML

Posted 2010/04/21

This blog post is about using LINQ to XML when the XML document has multiple namespaces defined. I’m using the Twitter API as example.

The sample XML

&lt;?xml version=&quot;1.0&quot; encoding=&quot;UTF-8&quot;?&gt;
&lt;feed xmlns:google=&quot;http://base.google.com/ns/1.0&quot; xml:lang=&quot;en-US&quot; xmlns:openSearch=&quot;http://a9.com/-/spec/opensearch/1.1/&quot; xmlns=&quot;http://www.w3.org/2005/Atom&quot; xmlns:twitter=&quot;http://api.twitter.com/&quot;&gt;
&lt;entry&gt;
  &lt;id&gt;tag:search.twitter.com,2005:12568401714&lt;/id&gt;
  &lt;published&gt;2010-04-21T10:07:04Z&lt;/published&gt;
  &lt;link type=&quot;text/html&quot; href=&quot;http://twitter.com/bergdaniel/statuses/12568401714&quot; rel=&quot;alternate&quot;/&gt;
  &lt;title&gt;The installation of DTCPing should come with a warning that says: &amp;quot;You have a long terrible journey ahead of you, Hobbit.&amp;quot;&lt;/title&gt;
  &lt;content type=&quot;html&quot;&gt;The installation of DTCPing should come with a warning that says: &amp;amp;quot;You have a long terrible journey ahead of you, Hobbit.&amp;amp;quot;&lt;/content&gt;
  &lt;updated&gt;2010-04-21T10:07:04Z&lt;/updated&gt;
  &lt;link type=&quot;image/png&quot; href=&quot;http://a3.twimg.com/profile_images/622795701/daniel-square_normal.jpg&quot; rel=&quot;image&quot;/&gt;
  &lt;twitter:geo&gt;
  &lt;/twitter:geo&gt;
  &lt;twitter:metadata&gt;
    &lt;twitter:result_type&gt;recent&lt;/twitter:result_type&gt;
  &lt;/twitter:metadata&gt;
  &lt;twitter:source&gt;&amp;lt;a href=&amp;quot;http://www.tweetdeck.com&amp;quot; rel=&amp;quot;nofollow&amp;quot;&amp;gt;TweetDeck&amp;lt;/a&amp;gt;&lt;/twitter:source&gt;
  &lt;twitter:lang&gt;en&lt;/twitter:lang&gt;
  &lt;author&gt;
    &lt;name&gt;bergdaniel (Daniel Berg)&lt;/name&gt;
    &lt;uri&gt;http://twitter.com/bergdaniel&lt;/uri&gt;
  &lt;/author&gt;
&lt;/entry&gt;
&lt;/feed&gt;

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

<entry>

<id>tag:search.twitter.com,2005:12568401714</id>

<title>The installation of DTCPing should come with a warning that says: &quot;You have a long terrible journey ahead of you, Hobbit.&quot;</title>

<content type="html">The installation of DTCPing should come with a warning that says: &amp;quot;You have a long terrible journey ahead of you, Hobbit.&amp;quot;</content>

<twitter:geo>

</twitter:geo>

<twitter:metadata>

<twitter:result_type>recent</twitter:result_type>

</twitter:metadata>

<twitter:source>&lt;a href=&quot;http://www.tweetdeck.com&quot; rel=&quot;nofollow&quot;&gt;TweetDeck&lt;/a&gt;</twitter:source>

<twitter:lang>en</twitter:lang>

<name>bergdaniel (Daniel Berg)</name>

<uri>http://twitter.com/bergdaniel</uri>

</author>

</entry>

</feed>

This is the partial XML result of the Twitter API query “http://search.twitter.com/search.atom?q=bergdaniel”. It includes a number of namespaces – the two most important being “http://www.w3.org/2005/atom” and “http://api.twitter.com/”.

Using LINQ to XML

public class Twitter
{
    private static XNamespace NAMESPACE_ATOM = &quot;http://www.w3.org/2005/Atom&quot;;
    private static XNamespace NAMESPACE_TWITTER = &quot;http://api.twitter.com/&quot;;

    public static List&lt;Tweet&gt; ParseTwitterFeed(string twitterUrlQuery)
    {
        XDocument tweetResults = XDocument.Load(twitterUrlQuery);

        var tweets = from tweet in tweetResults.Descendants(NAMESPACE_ATOM + &quot;entry&quot;)
                      select new Tweet
                      {
                          Author = tweet.Element(NAMESPACE_ATOM + &quot;author&quot;).Element(NAMESPACE_ATOM + &quot;name&quot;).Value,
                          Content = tweet.Element(NAMESPACE_ATOM + &quot;content&quot;).Value,
                          Published = (DateTime)tweet.Element(NAMESPACE_ATOM + &quot;updated&quot;),
                          Source = tweet.Element(NAMESPACE_TWITTER + &quot;source&quot;).Value
                      };

        return tweets.ToList&lt;Tweet&gt;();
    }

}

public class Twitter

{

private static XNamespace NAMESPACE_ATOM = "http://www.w3.org/2005/Atom";

private static XNamespace NAMESPACE_TWITTER = "http://api.twitter.com/";

public static List<Tweet> ParseTwitterFeed(string twitterUrlQuery)

{

XDocument tweetResults = XDocument.Load(twitterUrlQuery);

var tweets = from tweet in tweetResults.Descendants(NAMESPACE_ATOM + "entry")

select new Tweet

{

Author = tweet.Element(NAMESPACE_ATOM + "author").Element(NAMESPACE_ATOM + "name").Value,

Content = tweet.Element(NAMESPACE_ATOM + "content").Value,

Published = (DateTime)tweet.Element(NAMESPACE_ATOM + "updated"),

Source = tweet.Element(NAMESPACE_TWITTER + "source").Value

};

return tweets.ToList<Tweet>();

}

In order to query the XML with LINQ we need to define the namespaces and pass them as parameters along with the element names. Since the “atom”-namespace is the default namespace all elements that are not prefixed with <correspondingNamespace:someElement> need to pass the “atom”-namespace as parameter. The elements that are prefixed with <twitter:elementName> need to have the “twitter”-namespace passed as parameter.

Important

Make sure that the namespace is defined exactly as it is in the XML. If you miss a trailing slash (“http://api.twitter.com” instead of “http://api.twitter.com/”) you’ll end up with an NullReferenceException like this:

daniel

Developer