XPath : Get nodes where child node contains an attribute

Question

Suppose I have the following XML:

<book category="CLASSICS">
  <title lang="it">Purgatorio</title>
  <author>Dante Alighieri</author>
  <year>1308</year>
  <price>30.00</price>
</book>

<book category="CLASSICS">
  <title lang="it">Inferno</title>
  <author>Dante Alighieri</author>
  <year>1308</year>
  <price>30.00</price>
</book>

<book category="CHILDREN">
  <title lang="en">Harry Potter</title>
  <author>J K. Rowling</author>
  <year>2005</year>
  <price>29.99</price>
</book>

<book category="WEB">
  <title lang="en">XQuery Kick Start</title>
  <author>James McGovern</author>
  <author>Per Bothner</author>
  <author>Kurt Cagle</author>
  <author>James Linn</author>
  <author>Vaidyanathan Nagarajan</author>
  <year>2003</year>
  <price>49.99</price>
</book>

<book category="WEB">
  <title lang="en">Learning XML</title>
  <author>Erik T. Ray</author>
  <year>2003</year>
  <price>39.95</price>
</book>

I would like to do an xpath that gets back all book nodes that have a title node with a language attribute of "it".

My attempt looked something like this:

//book[title[@lang='it']]

But that didn't work. I expect to get back the nodes:

<book category="CLASSICS">
  <title lang="it">Purgatorio</title>
  <author>Dante Alighieri</author>
  <year>1308</year>
  <price>30.00</price>
</book>

<book category="CLASSICS">
  <title lang="it">Inferno</title>
  <author>Dante Alighieri</author>
  <year>1308</year>
  <price>30.00</price>
</book>

Any hints? Thanks in advance.

Answer 1

Try

//book[title/@lang = 'it']

This reads:

• get all book elements
  • that have at least one title
    • which has an attribute lang
      • with a value of "it"

You may find this helpful — it's an article entitled "XPath in Five Paragraphs" by Ronald Bourret.

But in all honesty, //book[title[@lang='it']] and the above should be equivalent, unless your XPath engine has "issues." So it could be something in the code or sample XML that you're not showing us.

Answer 2

//book[title[@lang='it']]

is actually equivalent to

 //book[title/@lang = 'it']

I tried it using vtd-xml, both expressions spit out the same result... what xpath processing engine did you use? I guess it has conformance issue Below is the code

import com.ximpleware.*;
public class test1 {
  public static void main(String[] s) throws Exception{
      VTDGen vg = new VTDGen();
      if (vg.parseFile("c:/books.xml", true)){
       VTDNav vn = vg.getNav();
       AutoPilot ap = new AutoPilot(vn);
       ap.selectXPath("//book[title[@lang='it']]");
                  //ap.selectXPath("//book[title/@lang='it']");

       int i;
       while((i=ap.evalXPath())!=-1){
        System.out.println("index ==>"+i);
       }
       /*if (vn.endsWith(i, "< test")){
       System.out.println(" good ");  
       }else
        System.out.println(" bad ");*/

      }
  }
}