Question

I have to do a case-insensitive XML search. I’ve written XPath expressions which are working fine, but when I use the translate function inside an XPath expression I get an error. Below are the XPath expressions that are working fine:

string upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string lower = "abcdefghijklmnopqrstuvwxyz";

string xpath = "/data/item[AID/@iskey='true' and AID/text() = 'fep'][not(*[@iskey][local-name() != 'AID' ])]";       

string xpath1 = "/data/item[translate('Aid','" + upper + "','" + lower + "')]";

And here is my XML:

<?xml version="1.0" encoding="utf-8"?>
<data>
<item>
 <AID iskey="true">fep</AID>
  <account>MS</account>
  </item>
</data>

I want to place the translate function in the first XPath expression like this:

 string xpath = "/data/item[translate('AID','" + upper + "','" + lower + "')/@iskey='true' and translate('AID','" + upper + "','" + lower + "')/text() = 'fep'][not(*[@iskey][local-name() != translate('aid','" + upper + "','" + lower + "') ])]";

When I do this, I get the following error:

Expression must evaluate to a node-set.

This xpath is working fine for me.

 string col="AID"; 
 string xpath = "/data/item[col/@iskey='true' and col/text() = 'fep'][not(*[@iskey][local-name() != 'col' ])]";   

Now my requirement is that the col value can be in any case upper case or lower case, so I want a change in my xpath with which it returns me the result irrespective of in which case data is present in the xml.
If a user gives aid or Aid or aiD it returns me the result.

Answer 1

The error is due to the fact that in your XPath expression you have a location step like this:

item['aid'/@isKey = 'true' ...]

The subexpression:

'aid'/@isKey

is syntactically illegal in XPath, because the left-hand-side of the / operator must be a node-set — here it is just a string.

You want to have an XPath expression like this — not the one you are generating at present:

/data/item
       [*[translate(name(), 'aid', 'AID') = 'AID']/@iskey='true'
      and
        *[translate(name(), 'aid', 'AID') = 'AID'] = 'fep'
         ]
          [not(*[@iskey]
                [translate(name(), 'aid', 'AID') != 'AID']
             )
         ]

XSLT – based verification:

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

 <xsl:variable name="vLower" select="'aid'"/>
 <xsl:variable name="vUpper" select="'AID'"/>

 <xsl:template match="node()|@*">
     <xsl:copy-of select=
      "/data/item
           [*[translate(name(), 'aid', 'AID') = 'AID']/@iskey='true'
          and
            *[translate(name(), 'aid', 'AID') = 'AID'] = 'fep'
             ]
              [not(*[@iskey]
                    [translate(name(), 'aid', 'AID') != 'AID']
                 )
             ]
      "/>
 </xsl:template>
</xsl:stylesheet>

When this transformation is applied on the provided XML document:

<data>
    <item>
        <AID iskey="true">fep</AID>
        <account>MS</account>
    </item>
</data>

the XPath expression is evaluated and the selected nodes (just one in this case) are copied to the output:

<item>
   <AID iskey="true">fep</AID>
   <account>MS</account>
</item>

Update:

The OP has difficulty understanding this solution. This is an example to show him that the solution works for any capitalisation of the string “aid”:

When the transformation above is applied on an XML document, that contains element names that are any capitalization of “aid” — such as this:

<data>
    <item>
        <aId iskey="true">fep</aId>
        <account>MS</account>
    </item>
</data>

again the expected result is produced:

<item>
   <aId iskey="true">fep</aId>
   <account>MS</account>
</item>

Update 2:

The OP still doesn’t understand the solution and claims that for a specific XML document — provided below — “I used your expression it returns null “

Here is the XML document as provided in the comment of the OP:

<data>
    <item>
        <aId iskey="true">fep</aId>
        <account>FG</account>
    </item>
</data>

When the same XSLT verification is run against this document, again the correct element is selected and output:

<item>
   <aId iskey="true">fep</aId>
   <account>FG</account>
</item>