XQuery return text node if it contains given keyword

Question

A test sample of my xml file is shown below:

test.xml

<feed>
  <entry>
    <title>Link ISBN</title>
    <libx:libapp xmlns:libx="http://libx.org/xml/libx2" />
  </entry>
  <entry>
    <title>Link Something</title>
    <libx:module xmlns:libx="http://libx.org/xml/libx2" />
  </entry>
</feed>

Now, I want to write an xquery which will find all <entry> elements which have <libx:libapp> as a child. Then, for all such entries return the title if the title contains a given keyword (such as Link). So, in my example xml document the xquery should return "Link ISBN".

My sample xquery is shown below:

samplequery.xq (here doc_name is the xml file shown above and libapp_matchkey is a keyword such as 'Link')

declare namespace libx='http://libx.org/xml/libx2';
declare variable $doc_name as xs:string external;
declare variable $libpp_matchkey as xs:string external;
let $feeds_doc := doc($doc_name)

for $entry in $feeds_doc/feed/entry
   (: test whether entry has libx:libapp child and has "Link" in its title child :)
   where ($entry/libx:libapp and $entry/title/text()[contains(.,$libapp_matchkey)])
    return $entry/title/text()

This xquery is returning null instead of the expected result 'Link ISBN'. Why is that?

I've replaced $food_doc declaration as /, corrected the $libapp_matchkey typo, and successfully runned it with your input sample. — user357812
– user357812, Commented Dec 14, 2010 at 21:43
Good question, +1. See my answer for a short and natural one-liner solution :) — Dimitre Novatchev
– Dimitre Novatchev, Commented Dec 14, 2010 at 22:14

Dimitre Novatchev · Accepted Answer · 2010-12-14 23:29:34Z

8

I want to write an xquery which will find all elements which have as a child. Then, for all such entries return the title if the title contains a given keyword (such as Link).

Just use:

/*/entry[libx:libapp]/title[contains(.,'Link')]/text()

Wrapping this XPath expression in XQuery we get:

declare namespace libx='http://libx.org/xml/libx2';
/*/entry[libx:libapp]/title[contains(.,'Link')]/text()

when applied on the provided XML document:

<feed> 
  <entry> 
    <title>Link ISBN</title> 
    <libx:libapp xmlns:libx="http://libx.org/xml/libx2" /> 
  </entry> 
  <entry> 
    <title>Link Something</title> 
    <libx:module xmlns:libx="http://libx.org/xml/libx2" /> 
  </entry> 
</feed>

the wanted, correct result is produced:

Link ISBN

edited Dec 14, 2010 at 23:29

answered Dec 14, 2010 at 22:13

Dimitre Novatchev

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10 Comments

sony Over a year ago

I see the following exception when I try this: for $entry in $feeds_doc/atom:feed/atom:entry return /*/$entry[libx:libapp]/title[contains(.,'Link')]/text() Exception in thread "main" java.io.IOException: Stopped at line 9, column 13: [XPDY0002] No context item set for 'root()'.

Dimitre Novatchev Over a year ago

@sony: There isn't any $entry in my answer -- You may get any possible exception on anything that isn't my answer, but why are you reporting this as a comment here?

sony Over a year ago

What does /* refer to ? I mean entry elements are inside <feed> element in the document. How are you referring to $feeds_doc/feed

Dimitre Novatchev Over a year ago

@sony: I have edited my answer to help you arive at a complete XQuery -- you may just execute it and you will get the wanted result.

Dimitre Novatchev Over a year ago

@sony: This is simple, basic XPath (and I seriously doubt that one can do XQuery without knowledge of XPath). /* selects the top element of any XML document (because in any well-formed XML document there must be a single top element). This is why we don't bother (and thus save time and space) to specify the name of the top element.

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