Selecting an XML subset with Nokogiri - xml-parsing

Question

For my first discovery of Nokogiri and XML parsing, I need to extract a list of Code items (with their children) provided a webservice. The document looks like this:
<message:Structure xmlns:common="http://www.SDMX.org/resources/SDMXML/schemas/v2_0/common" xmlns:structure="http://www.SDMX.org/resources/SDMXML/schemas/v2_0/structure" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:message="http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message" xsi:schemaLocation="http://www.SDMX.org/resources/SDMXML/schemas/v2_0/message SDMXMessage.xsd">
<message:Header>
<message:ID>70c32d97-bbd5-44c7-8bff-50a63abe07eb</message:ID>
<message:Test>false</message:Test>
<message:Prepared>2021-08-26T11:37:37</message:Prepared>
<message:Sender id="CH1">
<message:Name>CH1</message:Name>
</message:Sender>
</message:Header>
<message:CodeLists>
<structure:CodeList id="CL_LEISTUNGSART" version="1.0" agencyID="CH1" isFinal="true">
<structure:Name xml:lang="de">Leistungsart</structure:Name>
<structure:Name xml:lang="fr">Type prestation</structure:Name>
<structure:Name xml:lang="it">Tipo di prestazione</structure:Name>
<structure:Code value="01">
</structure:Code>
<structure:Code value="02">
<structure:Description xml:lang="de">Reguläre Unterstützung mit Zielvereinbarung</structure:Description>
<structure:Description xml:lang="fr">Aide financière régulière avec contrat d'insertion</structure:Description>
<structure:Description xml:lang="it">Assistenza regolare con contratto d’inserimento</structure:Description>
<structure:Annotations>
</structure:Annotations>
</structure:Code>
<structure:Code value="03">
</structure:Code>
<structure:Code value="04">
</structure:Code>
<structure:Code value="05">
</structure:Code>
<structure:Code value="10">
</structure:Code>
<structure:Code value="21">
</structure:Code>
<structure:Code value="22">
</structure:Code>
<structure:Code value="23">
</structure:Code>
<structure:Code value="25">
</structure:Code>
<structure:Code value="26">
</structure:Code>
<structure:Code value="32">
</structure:Code>
<structure:Code value="33">
</structure:Code>
<structure:Code value="34">
</structure:Code>
<structure:Code value="35">
</structure:Code>
<structure:Code value="36">
</structure:Code>
<structure:Code value="37">
</structure:Code>
<structure:Code value="40">
</structure:Code>
<structure:Code value="50">
</structure:Code>
<structure:Annotations>
</structure:Annotations>
</structure:CodeList>
<structure:CodeList id="CL_LEISTUNGSART" version="2.0" agencyID="CH1">
</structure:CodeList>
</message:CodeLists>
</message:Structure>
The request is: select the one CodeList from the structure where version is the highest value and isFinal is true, and then read the Code elements (with their children).
I can select the CodeList elements from the structure namespace:
document.css("structure|CodeList")
but then I get lost when trying to evaluate attributes version and isFinal.
Your help will be greatly appreciated!

Answer 1

For reasons you'll see below, this is not really an answer, but it's too long for a comment and may help to some extent.
In terms of pure xpath expressions, to get (for example), the French language translation of the structure:Name child node of the structure:CodeList node (which meets your two requirements), the following expression
//structure:CodeList[#version=max(//*[#isFinal="true"]/number(#version))]/structure:Name[#xml:lang="fr"]/text()
would output
Type prestation
and similarly for other languages or, for example structure:Description. Since the xml uses namespaces, for nokogiri you'll have to use something like
doc.xpath('//structure:CodeList[#version=max(//*[#isFinal="true"]/number(#version))]/structure:Name[#xml:lang="fr"]/text()',
'structure' => "http://www.SDMX.org/resources/SDMXML/schemas/v2_0/structure")
The problem is the use of the max() function in the expression. I can't test it myself right now, but max() is an xpath 2.0 function and my understanding is that only xpath 1.0 is supported.
One why to possibly address the issue of support for later xpath versions is to take a look here.