Creating an XML document with a namespaced root element with Nokogiri builder

Question

I'm implementing an exporter for an XML data format that requires namespaces. I'm using the Nokogiri XML Builder (version 1.4.0) to do this.

However, I can't get Nokogiri to create a root node with a namespace.

This works:

Nokogiri::XML::Builder.new { |xml| xml.root('xmlns:foobar' => 'my-ns-url') }.to_xml

<?xml version="1.0"?>
<root xmlns:foobar="my-ns-url"/>

As does this:

Nokogiri::XML::Builder.new do |xml| 
  xml.root('xmlns:foobar' => 'my-ns-url') { xml['foobar'].child }
end.to_xml

<?xml version="1.0"?>
<root xmlns:foobar="my-ns-url">
  <foobar:child/>
</root>

However, I need something like <foo:root> and this doesn't work:

Nokogiri::XML::Builder.new { |xml| xml['foobar'].root('xmlns:foobar' => 'my-ns-url') }.to_xml

NoMethodError: undefined method `namespace_definitions' for #<Nokogiri::XML::Document:0x11bfef8 name="document">

Namespaces have to be defined before use, apparently, so there's no way to add one to the root node.

I found a question about this on the Nokogiri mailing list, but it had no replies. Anyone have a solution?

Answer 1

require 'rubygems'
require 'nokogiri'

puts Nokogiri::XML::Builder.new { |xml| 
  xml.root("xmlns:foo"=>"url") {
    xml.parent.namespace = xml.parent.namespace_definitions.first
    xml['foo'].child
  }
}.to_xml

You cannot use xml['foo'] before the namespace is defined, ie before you pass it as an argument to the root not. Thus, the code above add the namespace after-the-fact to the root node.