From: 011netservice@gmail.com
Date: 2024-04-09
Subject: XPath-Samples.txt

歡迎來信交流, 訂購軟體需求.

#### Attributes with the name "ID" are not of type ID unless so defined in the DTD. 
https://stackoverflow.com/questions/19786770/how-can-i-get-a-node-by-id-in-xml

The DOM implementation must have information which defines which attributes are of type ID. 
Although attributes of type ID can be defined in either XSD schemas or DTDs, 
this version of the product only supports those defined in DTDs. 
Attributes with the name "ID" are not of type ID unless so defined in the DTD. 

Implementations where it is unknown whether the attributes are of type ID are expected to return null.

In fact, you have to modify your XML file for specifying what you mean by 'ID'. 
If you don't want to do that, use a select method with an XPath.

So you need instead :
/* sample
string filePath = "D:\\XML\\LanguagePack.xml";
var fileInfo = new FileInfo(filePath);
var xmlDocument = new XmlDocument();
xmlDocument.Load(fileInfo.FullName);

var node = xmlDocument.SelectSingleNode("//*[@id='10001']");
return node.InnerText; // return 'Word1_French'
*/

#### 
XML File (inventory.xml)
<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="myfile.xsl" ?>
<bookstore specialty="novel">
  <book style="autobiography">
    <author>
      <first-name>Joe</first-name>
      <last-name>Bob</last-name>
      <award>Trenton Literary Review Honorable Mention</award>
    </author>
    <price>12</price>
  </book>
  <book style="textbook">
    <author>
      <first-name>Mary</first-name>
      <last-name>Bob</last-name>
      <publication>Selected Short Stories of
        <first-name>Mary</first-name>
        <last-name>Bob</last-name>
      </publication>
    </author>
    <editor>
      <first-name>Britney</first-name>
      <last-name>Bob</last-name>
    </editor>
    <price>55</price>
  </book>
  <magazine style="glossy" frequency="monthly">
    <price>2.50</price>
    <subscription price="24" per="year"/>
  </magazine>
  <book style="novel" id="myfave">
    <author>
      <first-name>Toni</first-name>
      <last-name>Bob</last-name>
      <degree from="Trenton U">B.A.</degree>
      <degree from="Harvard">Ph.D.</degree>
      <award>Pulitzer</award>
      <publication>Still in Trenton</publication>
      <publication>Trenton Forever</publication>
    </author>
    <price intl="Canada" exchange="0.7">6.50</price>
    <excerpt>
      <p>It was a dark and stormy night.</p>
      <p>But then all nights in Trenton seem dark and
      stormy to someone who has gone through what
      <emph>I</emph> have.</p>
      <definition-list>
        <term>Trenton</term>
        <definition>misery</definition>
      </definition-list>
    </excerpt>
  </book>
  <my:book xmlns:my="uri:mynamespace" style="leather" price="29.50">
    <my:title>Who's Who in Trenton</my:title>
    <my:author>Robert Bob</my:author>
  </my:book>
</bookstore>


This topic reviews the syntax examples that appear throughout the XPath Reference. 
All are based on the Sample XML File for XPath Syntax (inventory.xml). 
For an example of using an XPath expression in a test file, see "Example of Unions ( | )", at the bottom of this topic.

Expression		Refers to
./author		All <author> elements within the current context. Note that this is equivalent to the expression in the next row.
author			All <author> elements within the current context.
first.name		All <first.name> elements within the current context.
/bookstore		The document element (<bookstore>) of this document.
//author		All <author> elements in the document.
book[/bookstore/@specialty=@style]	All <book> elements whose style attribute value is equal to the specialty attribute value of the <bookstore> element at the root of the document.
author/first-name	All <first-name> elements that are children of an <author> element.
bookstore//title	All <title> elements one or more levels deep in the <bookstore> element (arbitrary descendants). Note that this is different from the expression in the next row.
bookstore/*/title	All <title> elements that are grandchildren of <bookstore> elements.
bookstore//book/excerpt//emph	All <emph> elements anywhere inside <excerpt> children of <book> elements, anywhere inside the <bookstore> element.
.//title		All <title> elements one or more levels deep in the current context. Note that this situation is essentially the only one in which the period notation is required.
author/*		All elements that are the children of <author> elements.
book/*/last-name	All <last-name> elements that are grandchildren of <book> elements.
*/*				All grandchildren elements of the current context.
*[@specialty]	All elements with the specialty attribute.
@style			The style attribute of the current context.	
price/@exchange	The exchange attribute on <price> elements within the current context.
price/@exchange/total	Returns an empty node set, because attributes do not contain element children. This expression is allowed by the XML Path Language (XPath) grammar, but is not strictly valid.
book[@style]	All <book> elements with style attributes, of the current context.
book/@style		The style attribute for all <book> elements of the current context.
@*	All attributes of the current element context.
./first-name	All <first-name> elements in the current context node. Note that this is equivalent to the expression in the next row.
first-name		All <first-name> elements in the current context node.
author[1]		The first <author> element in the current context node.
author[first-name][3]	The third <author> element that has a <first-name> child.
my:book			The <book> element from the my namespace.
my:*			All elements from the my namespace.
@my:*			All attributes from the my namespace (this does not include unqualified attributes on elements from the my namespace).

Note that indexes are relative to the parent. 	Consider the following data:
<x>
  <y/>
  <y/>
</x>
<x>
  <y/>
  <y/>
</x>

Expression			Refers to
x/y[1]				The first <y> child of each <x>. This is equivalent to the expression in the next row.
x/y[position() = 1]	The first <y> child of each <x>.
(x/y)[1]			The first <y> from the entire set of <y> children of <x> elements.
x[1]/y[2]			The second <y> child of the first <x>.

The remaining examples refer to the Sample XML file for XPath.
Expression					Refers to
book[last()]				The last <book> element of the current context node.
book/author[last()]			The last <author> child of each <book> element of the current context node.
(book/author)[last()]		The last <author> element from the entire set of <author> children of <book> elements of the current context node.
book[excerpt]				All <book> elements that contain at least one <excerpt> element child.
book[excerpt]/title			All <title> elements that are children of <book> elements that also contain at least one <excerpt> element child.
book[excerpt]/author[degree]	All <author> elements that contain at least one <degree> element child, and that are children of <book> elements that also contain at least one <excerpt> element.
book[author/degree]			All <book> elements that contain <author> children that in turn contain at least one <degree> child.
author[degree][award]		All <author> elements that contain at least one <degree> element child and at least one <award> element child.
author[degree and award]	All <author> elements that contain at least one <degree> element child and at least one <award> element child.
author[(degree or award) and publication]	All <author> elements that contain at least one <degree> or <award> and at least one <publication> as the children
author[degree and not(publication)]	All <author> elements that contain at least one <degree> element child and that contain no <publication> element children.
author[not(degree or award) and publication]	All <author> elements that contain at least one <publication> element child and contain neither <degree> nor <award> element children.
author[last-name = "Bob"]	All <author> elements that contain at least one <last-name> element child with the value Bob.
author[last-name[1] = "Bob"]	All <author> elements where the first <last-name> child element has the value Bob. Note that this is equivalent to the expression in the next row.
author[last-name [position()=1]= "Bob"]	All <author> elements where the first <last-name> child element has the value Bob.
degree[@from != "Harvard"]	All <degree> elements where the from attribute is not equal to "Harvard".
author[. = "Matthew Bob"]	All <author> elements whose value is Matthew Bob.
author[last-name = "Bob" and ../price &gt; 50]	All <author> elements that contain a <last-name> child element whose value is Bob, and a <price> sibling element whose value is greater than 50.
book[position() &lt;= 3]	The first three books (1, 2, 3).
author[not(last-name = "Bob")]	All <author> elements that do no contain <last-name> child elements with the value Bob.
author[first-name = "Bob"]	All <author> elements that have at least one <first-name> child with the value Bob.
author[* = "Bob"]			all author elements containing any child element whose value is Bob.
author[last-name = "Bob" and first-name = "Joe"]	All <author> elements that has a <last-name> child element with the value Bob and a <first-name> child element with the value Joe.
price[@intl = "Canada"]	All <price> elements in the context node which have an intl attribute equal to "Canada".
degree[position() &lt; 3]	The first two <degree> elements that are children of the context node.
p/text()[2]					The second text node in each <p> element in the context node.
ancestor::book[1]			The nearest <book> ancestor of the context node.
ancestor::book[author][1]	The nearest <book> ancestor of the context node and this <book> element has an <author> element as its child.
ancestor::author[parent::book][1]	The nearest <author> ancestor in the current context and this <author> element is a child of a <book> element.

Example of Unions ( | )
To demonstrate the union operation, we use the following XPath expression:

x | y/x

selects all the <x> elements whose values are green or blue in the following XML file:
XML File (data1.xml)
<?xml version='1.0'?>
<?xml-stylesheet type="text/xsl" href="union.xsl"?>
<root>
   <x>green</x>
   <y>
      <x>blue</x>
      <x>blue</x>
   </y>
   <z>
      <x>red</x>
      <x>red</x>
   </z>
   <x>green</x>
</root>

XSLT File (union.xsl)
<?xml version='1.0'?>
<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:template match="root">
   <xsl:for-each select="x | y/x">
      <xsl:value-of select="."/>,
      <xsl:if test="not(position()=last())">,</xsl:if>
   </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

Formatted Output
green,blue,blue,green

Processor Output
<?xml version="1.0" encoding="UTF-16"?>green,blue,blue,green