.NET, XPath, and XmlNamespaceManager

Noah — Thu, 03 Dec 2009 19:16:49 GMT

Take the following XML fragment

        1: <?xml version="1.0" encoding="iso-8859-1"?>

       2: <con:search-results 

       3: xmlns:con="http://namespace.contoso.com/business-objects" 

       4: xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

       5: xsi:noNamespaceSchemaLocation="http://www.contoso.com/dtd/syndication/biz-objects.xsd">

       6:     <con:search-query>ipod</con:search-query>

       7:     <con:result-count>2207</con:result-count>

       8:     <con:start-index>0</con:start-index>

       9:     <con:result-count>15</con:result-count>

      10:     <con:results>

      11:         <con:result>

      12:             ...

      13:

Now suppose you loaded this XML into an XmlDocument, how would you query for all the <con:result> nodes? Using XPath you’d write something like

       1: /search-results/results/result

So you might try writing something like

       1: XmlDocument doc = new XmlDocument();

       2: doc.LoadXml(response);

       3: var resultNodes = doc.SelectNodes("/search-results/results/result");

but you would find that resuldNodes would be null. You have to instantiate an XmlNamespaceManager to help correctly maneuver your namespaces. That’s done like so:

       1: XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlDoc.NameTable);

       2: nsmgr.AddNamespace("con", "http://namespace.contoso.com/business-objects");

Then you would query your xml like so:

       1: var resultNodes = doc.SelectNodes("/con:search-results/con:results/con:result")

That took me a little searching to dig up, but it makes sense, right?