C# and XPath - how to query

Question

Hi folks,

I have an XML-File, which has the following structure:

<mediawiki ...>
  <siteinfo>...</siteinfo>
  <page>
    <title>The Title</title>
    <id>42</id>
    ...
  </page>
  ... more page items ...
</mediawiki>

I red a bit about XPath-Query and wrote the following code:

_xmlArticlesDocument = new XmlDocument();
_xmlArticlesDocument.Load(xmlArticlesFileName);

Now I want to get a grip on a page Element with a given id-Subelement. So I wrote:

XmlNode node = _xmlArticlesDocument.DocumentElement.SelectSingleNode
               ("//mediawiki/page[id=" + id.ToString() + "]");

but node is always null. I have tried several querys, including "page/id", "page", "/page", "//page" to get anything, but node is always null. I have checked via quick inspection the _xmlArticlesDocument variable and it contains the correct XML-file with the expected structure.

It seems to me, that I have missed something very basic, but have no idea what. Maybe someone here has an idea?

Thanks in advance, Frank

Answer 1

Have you tried:

_xmlArticlesDocument.DocumentElement.SelectSingleNode
               ("page[id='" + id.ToString() + "']"); // Note the single quotes

Also, if any of the XML nodes are in a namespace that is not the default one (i.e. <mediawiki xmlns="whatever">) then you are also going to need an XmlNamespaceManager.

Answer 2

The query looks right on the basis of what you shown us so far. However I suspect behin the "..." on the mediawiki element there is a xmlns="...." attribute right?

That'll be what is tripping you up I suspect. You will need code like this:-

 XmlNamespaceManager nsmgr = new XmlNamespaceManager(_xmlArticlesDocument.NameTable);
 nsmgr.AddNamespace("a", "the-namespace-in-them-xmlns-attribute");
 XmlNode page = _xmlArticlesDocument.SelectSingleNode(String.Format("//a:page[id={0}]", id), nsmgr);

Answer 3

Check out Linq to XML. I am a XML noob too, and I am finding it to be easier, the XMLDocument.