title: Query an XmlDocument without getting a 'Namespace prefix is not defined' problem
body: <p>I've got an Xml document that both defines and references some namespaces. I load it into an XmlDocument object and to the best of my knowledge I create a XmlNamespaceManager object with which to query Xpath against. Problem is I'm getting XPath exceptions that the namespace "my" is not defined. How do I get the namespace manager to see that the namespaces I am referencing are already defined. Or rather how do I get the namespace definitions from the document to the namespace manager. </p>
  
  <p>Furthermore tt strikes me as strange that you have to provide a namespace manager to the document which you create from the documents nametable in the first place. Even if you need to hardcode manual namespaces why can't you add them directly to the document. Why do you always have to pass this namespace manager with every single query? What can't XmlDocument just know?</p>
  
  <p>Code:</p>
  
  <pre><code>XmlDocument xmlDoc = new XmlDocument();
  xmlDoc.Load(programFiles + @"Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\FEATURES\HfscBookingWorkflow\template.xml");
  XmlNamespaceManager ns = new XmlNamespaceManager(xmlDoc.NameTable);
  
  XmlNode referenceNode = xmlDoc.SelectSingleNode("/my:myFields/my:ReferenceNumber", ns);
  referenceNode.InnerXml = this.bookingData.ReferenceNumber;
  
  XmlNode titleNode = xmlDoc.SelectSingleNode("/my:myFields/my:Title", ns);
  titleNode.InnerXml = this.bookingData.FamilyName;
  </code></pre>
  
  <p>Xml:</p>
  
  <pre><code>  &lt;?xml version="1.0" encoding="UTF-8" ?&gt; 
    &lt;?mso-infoPathSolution name="urn:schemas-microsoft-com:office:infopath:Inspection:-myXSD-2010-01-15T18-21-55" solutionVersion="1.0.0.104" productVersion="12.0.0" PIVersion="1.0.0.0" ?&gt; 
    &lt;?mso-application progid="InfoPath.Document" versionProgid="InfoPath.Document.2"?&gt; 
    &lt;my:myFields xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2010-01-15T18:21:55" xmlns:xd="http://schemas.microsoft.com/office/infopath/2003"&gt;
    &lt;my:DateRequested xsi:nil="true" /&gt; 
    &lt;my:DateVisited xsi:nil="true" /&gt; 
    &lt;my:ReferenceNumber /&gt; 
    &lt;my:FireCall&gt;false&lt;/my:FireCall&gt; 
  </code></pre>
  
  <p><strong>Update:</strong></p>
  
  <pre><code>ns.AddNamespace("xsi", "http://www.w3.org/2001/XMLSchema-instance");
  ns.AddNamespace("xhtml", "http://www.w3.org/1999/xhtml");
  ns.AddNamespace("xd", "http://schemas.microsoft.com/office/infopath/2003");
  ns.AddNamespace("my", "http://schemas.microsoft.com/office/infopath/2003/myXSD/2010-01-15T18:21:55");
  </code></pre>
  
  <p>This does the job, but it mean's I have to hard code to this particular xml schema. This schema represents an infopath form template. In particular the my namespace url will be different for every form template so I really don't want to hardcode this. It would be nice to find a clean way to get this namespace from the xml without resorting to RegEx.</p>
  
  <p>I was hoping that the XmlNamespaceManager would just sort of pick up the namespace definitions form the NameTable. I mean their in the Xml but I still have to define them.</p>