.NET & XML

XmlNode

XmlNode defines two methods, with two overloads each, to allow navigation via XPath. SelectSingleNode( ) returns a single XmlNode that matches the given XPath, and SelectNodes( ) returns an XmlNodeList.

Selecting a single node

SelectSingleNode( ) returns a single XmlNode that matches the given XPath expression. If more than one node matches the expression, the first one is returned; the definition of “first” depends on the order of the axis used. The context node of the XPath query is set to the XmlNode instance on which the method is invoked.

One overload of SelectSingleNode( ) takes just the XPath expression. The other one takes the XPath expression and an XmlNamespaceManager. The XmlNamespaceManager is used to resolve any prefixes in the XPath expression.

Example 6-2 shows a simple program that selects a single node from an XML document and writes it to the console, with human-readable formatting.

Example 6-2. Program to execute an XPath query on a document

using System;
using System.Xml;
using System.Xml.XPath;

public class XPathQuery {

  public static void Main(string [ ] args) {

    string filename = args[0];
    string xpathExpression = args[1]; 

    XmlDocument document = new XmlDocument( );
    document.Load(filename);

    XmlTextWriter writer = new XmlTextWriter(Console.Out);
    writer.Formatting = Formatting.Indented;

    XmlNode node = document.SelectSingleNode(xpathExpression);
    node.WriteTo(writer);

    writer.Close( );
  }
}

Because SelectSingleNode( ) is called on the XmlNode instance that represents ...