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 structu

Answer 1

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

Answer 2

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.