XmlNode.SelectSingleNode Method (String)

 

Selects the first XmlNode that matches the XPath expression.

Namespace:   System.Xml
Assembly:  System.Xml (in System.Xml.dll)

public XmlNode SelectSingleNode(
	string xpath
)

Parameters

xpath
Type: System.String

The XPath expression. See XPath Examples.

Return Value

Type: System.Xml.XmlNode

The first XmlNode that matches the XPath query or null if no matching node is found.

Exception Condition
XPathException

The XPath expression contains a prefix.

If the XPath expression requires namespace resolution, you must use the SelectSingleNode overload which takes an XmlNamespaceManager as its argument. The XmlNamespaceManager is used to resolve namespaces.

System_CAPS_noteNote

If the XPath expression does not include a prefix, it is assumed that the namespace URI is the empty namespace. If your XML includes a default namespace, you must still use the XmlNamespaceManager and add a prefix and namespace URI to it; otherwise, you will not get a selected node. For more information, see Select Nodes Using XPath Navigation.

System_CAPS_noteNote

A common issue when formulating XPath expressions is how to include a single quote (') or double quote (") in the expression. If you have to search for a value that includes a single quote, you must enclose the string in double quotes. If you need to search for a value that includes a double quote, you must enclose the string in single quotes.

For example, suppose you have the following XML:

<bookstore>
  <book>
    <title>&apos;Emma&apos;</title>
  </book>
</bookstore>

The following Visual Basic code selects an element that contains single quotes:

book = root.SelectSingleNode("descendant::book[title=""'Emma'""]")

This method is a Microsoft extension to the Document Object Model (DOM).

The following example changes the price of the first Jane Austen book.

using System;
using System.IO;
using System.Xml;

public class Sample {

  public static void Main() {

    XmlDocument doc = new XmlDocument();
    doc.Load("booksort.xml");

    XmlNode book;
    XmlNode root = doc.DocumentElement;

    book=root.SelectSingleNode("descendant::book[author/last-name='Austen']");

    //Change the price on the book.
    book.LastChild.InnerText="15.95";

    Console.WriteLine("Display the modified XML document....");
    doc.Save(Console.Out);    
  }
}

The example uses the file, booksort.xml, as input.


<?xml version="1.0"?>
<!-- A fragment of a book store inventory database -->
<bookstore xmlns:bk="urn:samples">
  <book genre="novel" publicationdate="1997" bk:ISBN="1-861001-57-8">
    <title>Pride And Prejudice</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>24.95</price>
  </book>
  <book genre="novel" publicationdate="1992" bk:ISBN="1-861002-30-1">
    <title>The Handmaid's Tale</title>
    <author>
      <first-name>Margaret</first-name>
      <last-name>Atwood</last-name>
    </author>
    <price>29.95</price>
  </book>
  <book genre="novel" publicationdate="1991" bk:ISBN="1-861001-57-6">
    <title>Emma</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>19.95</price>
  </book>
  <book genre="novel" publicationdate="1982" bk:ISBN="1-861001-45-3">
    <title>Sense and Sensibility</title>
    <author>
      <first-name>Jane</first-name>
      <last-name>Austen</last-name>
    </author>
    <price>19.95</price>
  </book>
</bookstore>

.NET Framework
Available since 1.1
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