Nokogiri: controlling element prefix for new child elments

Question

I have an xml document like this:

<?xml version="1.0" encoding="UTF-8"?>
<foo:root xmlns:foo="http://abc.com#" xmlns:bar="http://def.com" xmlns:ex="http://ex.com">
  <foo:element foo:attribute="attribute_value">
    <bar:otherElement foo:otherAttribute="otherAttributeValue"/>
  </foo:element>
</foo:root>

I need to add child elements to the element so that it looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<foo:root xmlns:foo="http://abc.com#" xmlns:bar="http://def.com" xmlns:ex="http://ex.com">
  <foo:element foo:attribute="attribute_value">
    <bar:otherElement foo:otherAttribute="otherAttributeValue"/>
    <bar:otherElement foo:otherAttribute="newAttributeValue"/>
    <ex:yetAnotherElement foo:otherAttribute="yetANewAttributeValue"/>
  </foo:element>
</foo:root>

I can add elements in the correct location using the following:

require 'rubygems'
require 'nokogiri'
doc = Nokogiri::XML::Document.parse(File.open("myfile.xml"))
el = doc.at_xpath('//foo:element')

newEl = Nokogiri::XML::Node.new("otherElement", doc)            
newEl["foo:otherAttribute"] = "newAttributeValue"
el.add_child(newEl)

newEl = Nokogiri::XML::Node.new("yetAnotherElement", doc)           
newEl["foo:otherAttribute"] = "yetANewAttributeValue"
el.add_child(newEl)

However the prefix of the new elements is always "foo":

<foo:root xmlns:foo="http://abc.com#" xmlns:bar="http://def.com" xmlns:ex="http://ex.com">
  <foo:element foo:attribute="attribute_value">
    <bar:otherElement foo:otherAttribute="otherAttributeValue" /> 
    <foo:otherElement foo:otherAttribute="newAttributeValue" /> 
    <foo:yetAnotherElement foo:otherAttribute="yetANewAttributeValue" /> 
  </foo:element>
</foo:root>

How can I set the prefix on the element name for these new child elements? Thanks, Eoghan

Answer 1

(removed bit about defining namespace, orthogonal to question and fixed in edit)

just add a few lines to your code, and you get the result desired:

require 'rubygems'
require 'nokogiri'
doc = Nokogiri::XML::Document.parse(File.open("myfile.xml"))
el = doc.at_xpath('//foo:element')

newEl = Nokogiri::XML::Node.new("otherElement", doc)            
newEl["foo:otherAttribute"] = "newAttributeValue"
# ADDITIONAL CODE
newEl.namespace = doc.root.namespace_definitions.find{|ns| ns.prefix=="bar"}
#
el.add_child(newEl)

newEl = Nokogiri::XML::Node.new("yetAnotherElement", doc)           
newEl["foo:otherAttribute"] = "yetANewAttributeValue"
# ADDITIONAL CODE
newEl.namespace = doc.root.namespace_definitions.find{|ns| ns.prefix == "ex"}
#
el.add_child(newEl)

and the result:

<?xml version="1.0" encoding="UTF-8"?>
<foo:root xmlns:abc="http://abc.com#" xmlns:def="http://def.com" xmlns:ex="http://ex.com" xmlns:foo="http://foo.com" xmlns:bar="http://bar.com">
  <foo:element foo:attribute="attribute_value">
    <bar:otherElement foo:otherAttribute="otherAttributeValue"/>
    <bar:otherElement foo:otherAttribute="newAttributeValue"/>
    <ex:yetAnotherElement foo:otherAttribute="yetANewAttributeValue"/>
  </foo:element>
</foo:root>