Adding namespace using Nokogiri's XML Builder

Question

I have been wrecking my head for a few hours but I can't seem to determine how to add XMLNS namespace whilst using the Nokogiri XML Builder class to construct a XML structure.

For instance, consider the XML sample below: I can create everything between the GetQuote tags but creating the "p:ACMRequest" remains a mystery.

I came across this reference, https://gist.github.com/428455/7a15f84cc08c05b73fcec2af49947d458ae3b96a, that still doesn't make sense to me. Even referring to the XML documentation,http://www.w3.org/TR/xml-names/, didn't make much sense either.

<?xml version="1.0" encoding="UTF-8"?>
<p:ACMRequest xmlns:p="http://www.acme.com" xmlns:p1="http://www.acme.com/datatypes" xmlns:p2="http://www.acme.com/ACMRequestdatatypes" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.acme.com ACM-req.xsd ">
  <GetQuote>
    <Request>
      <ServiceHeader>
        ...
        ...
      </ServiceHeader>
    </Request>
    <From>
      ...
      ...
    </From>
    <Details>
      ...
      ...
    </Details>
  </GetQuote>
</p:ACMRequest>

Daniel · Accepted Answer · 2020-04-20 21:33:03Z

16

The Nokogiri documentation page says:

Namespaces are added similarly to attributes. Nokogiri::XML::Builder assumes that when an attribute starts with “xmlns”, it is meant to be a namespace:
   builder = Nokogiri::XML::Builder.new { |xml|
     xml.root('xmlns' => 'default', 'xmlns:foo' => 'bar') do
       xml.tenderlove
     end
   }
   puts builder.to_xml
Will output XML like this:
   <?xml version="1.0"?>
   <root xmlns:foo="bar" xmlns="default">
     <tenderlove/>
   </root>

Applying this to your specific question, simply do:

require 'nokogiri'
NS = {
  "xmlns:p"   => "http://www.acme.com",
  "xmlns:p1"  => "http://www.acme.com/datatypes",
  "xmlns:p2"  => "http://www.acme.com/ACMRequestdatatypes",
  "xmlns:xsi" => "http://www.w3.org/2001/XMLSchema-instance",
}
builder = Nokogiri::XML::Builder.new { |xml|
  xml.ACMRequest(NS) do
    xml.GetQuote
  end
}
puts builder.to_xml

#=> <?xml version="1.0"?>
#=> <ACMRequest xmlns:p="http://www.acme.com" xmlns:p1="http://www.acme.com/datatypes" xmlns:p2="http://www.acme.com/ACMRequestdatatypes" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
#=>   <GetQuote/>
#=> </ACMRequest>

As for the namespace prefix on the root element itself…

<p:ACMRequest xmlns:p="…">…</p:ACMRequest>

…I cannot figure out how to apply a namespace prefix to the first element in Nokogiri during creation. Instead, you have to apply the namespace after creating the document:

root = builder.doc.root
acme = root.namespace_definitions.find{ |ns| ns.href==NS["xmlns:p"] }
root.namespace = acme
puts builder.to_xml

#=> <?xml version="1.0"?>
#=> <p:ACMRequest xmlns:p="http://www.acme.com" xmlns:p1="http://www.acme.com/datatypes" xmlns:p2="http://www.acme.com/ACMRequestdatatypes" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">atypes" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
#=>   <GetQuote/>
#=> </p:ACMRequest>

Alternatively, you can cheat:

# This happens to work for now, but I doubt you should rely upon it.
builder.doc.root.name = "p:ACMRequest"

Per "How to create an XML document with a namespaced root element with Nokogiri Builder" you can alternatively do this during creation via a small hack:

builder = Nokogiri::XML::Builder.new { |xml|
  xml.ACMRequest(NS) do
   xml.parent.namespace = … # find the ns in xml.parent.namespace_definitions
   # …
  end
end

edited Apr 20, 2020 at 21:33

Daniel

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answered Nov 4, 2011 at 15:10

Phrogz

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4 Comments

Phrogz Over a year ago

@muistooshort No; the first four blocks (quote, code, quote, code) are all from the page. I'll indent them all for increased clarity.

mu is too short Over a year ago

It looked like an editing mistake but it was just a Markdown artifact. You can make a "code block inside a blockquote" work if you use enough leading spaces on the code block and enough > for the blockquote. I think I fixed it, I'm just feeling a bit OCD this morning

ekynox Over a year ago

Sorry for the late response. @Phrogz thanks for your extensive response. My experience with XML has been rather limited but your response did clear up a few other questions I had as well. I have lost count of how many times I have looked at the Nokogiri documentation but its not till someone else explains it that things makes sense. :-) yup i did notice the typo in the code block too :-)

XP84 Over a year ago

Congratulations, now the first hit on Google for that is this page.

duncan · Accepted Answer · 2013-07-26 08:09:53Z

13

require 'nokogiri'
NS = {
  "xmlns:p"   => "http://www.acme.com",
  "xmlns:p1"  => "http://www.acme.com/datatypes",
  "xmlns:p2"  => "http://www.acme.com/ACMRequestdatatypes",
  "xmlns:xsi" => "http://www.w3.org/2001/XMLSchema-instance",
}
builder = Nokogiri::XML::Builder.new { |xml|
  xml['p'].ACMRequest(NS) do
    xml.GetQuote
  end
}
puts builder.to_xml

Produces:

<?xml version="1.0"?>
<p:ACMRequest xmlns:p="http://www.acme.com" xmlns:p1="http://www.acme.com/datatypes" xmlns:p2="http://www.acme.com/ACMRequestdatatypes" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <p:GetQuote/>
</p:ACMRequest>

This is documented in the builder API: http://nokogiri.org/Nokogiri/XML/Builder.html:

Referencing declared namespaces

Tags that reference non-default namespaces (i.e. a tag “foo:bar”) can be built by using the Nokogiri::XML::Builder#[] method.

answered Jul 26, 2013 at 8:09

duncan

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1 Comment

RajaRaviVarma Over a year ago

Caution: This adds the namespace (p) in all the nested tags.

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