Obtain nodes that don't have specific ancestor xml xpath

Question

I would like to have xpath, that obtains nodes, that don't have ancestor, which is first descendant of specific node.

Let's assume we have xml document like this:

<a>
  <b>This node</b>
  <c>
    <a>
      <b>not this</b>
      <g>
        <b>not this</b>
      </g>
    </a>
    <a>
      <b>This node</b>
      <c/>
    </a>
  </c>
</a>


<a>
  <c>
    <a>
      <b>not this</b>
    </a>
    <a>
      <b>This node</b> 
    </a>
    <a>
      <b>This node</b> 
    </a>
    <a>
      <b>This node</b> 
    </a>
  </c>
</a>


<d>
  <b>This node</b>
</d>

I would like to select all b nodes in document that don't have as their ancestor node //a/c/a[1].

Answer 1

I would like to select all b nodes in document that don't have as their ancestor node //a/c/a[1]

Use this XPath expression:

//b[not(ancestor::a
             [parent::c[parent::a]
            and
              not(preceding-sibling::a)
             ]
       )
   ]

This selects all b elements in the document that don't have ancestor a that has a parent c that has parent a and the a ancestor that has parent c is not the first a child of its parent.

Given the following XML document (based on the provided, but made well-formed and also put identifying text in the nodes that should be selected):

<t>
    <a>
        <b>This node 1</b>
        <c>
            <a>
                <b>not this</b>
                <g>
                    <b>not this</b>
                </g>
            </a>
            <a>
                <b>This node 2</b>
                <c/>
            </a>
        </c>
    </a>
    <a>
        <c>
            <a>
                <b>not this</b>
            </a>
            <a>
                <b>This node 3</b>
            </a>
            <a>
                <b>This node 4</b>
            </a>
            <a>
                <b>This node 5</b>
            </a>
        </c>
    </a>
    <d>
        <b>This node 6</b>
    </d>
</t>

exactly the wanted 6 b elements are selected.

Verification using XSLT:

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output omit-xml-declaration="yes" indent="yes"/>

 <xsl:template match="/">
 <xsl:copy-of select=
 "//b[not(ancestor::a
             [parent::c[parent::a]
            and
              not(preceding-sibling::a)
             ]
         )
     ]

 "/>
 </xsl:template>
</xsl:stylesheet>

when this transformation is applied on the above XML document, exactly the wanted b elements are selected and copied to the output. The wanted, correct result is produced:

<b>This node 1</b>
<b>This node 2</b>
<b>This node 3</b>
<b>This node 4</b>
<b>This node 5</b>
<b>This node 6</b>