How to convert XML to hash in Rails where empty array and nil values are preserved

Question

When I convert an XML structure to hash with Hash.from_xml(@xml) in Rails, the parser does not distinguish between empty arrays and nil values, whereas the XML depicts nodes that are immediately terminated with \ to be empty arrays, e.g. <audio_languages/> vs. those with attribute nil="true" to be interpreted as nil values.

The XML structure (which I have control over on how to generate) looks like this:

<response>
  <medias>
    <media>
      <id>1</id>
      <name>Media-1</name>
      <audio_languages/>
      <avg_rating nil="true"></avg_rating>
    </media>
    <media>
      <id>2</id>
      <name>Media-2</name>
      <audio_languages/>
      <avg_rating nil="true"></avg_rating>
    </media>
  </medias>
</response>

The expected output from Hash.from_xml(@xml) would be:

{"response"=>{"medias"=>{"media"=>[{"id"=>"1", "name"=>"Media-1", "audio_languages"=>[], "avg_rating"=>nil}, {"id"=>"2", "name"=>"Media-2", "audio_languages"=>[], "avg_rating"=>nil}]}}}

instead, I get nil values for audio_languages and avg_rating:

{"response"=>{"medias"=>{"media"=>[{"id"=>"1", "name"=>"Media-1", "audio_languages"=>nil, "avg_rating"=>nil}, {"id"=>"2", "name"=>"Media-2", "audio_languages"=>nil, "avg_rating"=>nil}]}}}

score 0 · Accepted Answer · answered Mar 28 '13 at 00:00

I ended up parsing the nodes using libxml and I am checking if the nodes has the signature I am looking for in order to figure out if I want to convert as an empty array vs. a nil value.

# Usage: Hash.from_xml_with_libxml(xml)
require 'xml/libxml'
# adapted from 
# http://movesonrails.com/articles/2008/02/25/libxml-for-active-resource-2-0

class Hash 
  class << self
    def from_xml_with_libxml(xml, strict=true) 
      LibXML::XML.default_load_external_dtd = false
      LibXML::XML.default_pedantic_parser   = strict
      result = LibXML::XML::Parser.string(xml).parse 
      return { result.root.name.to_s => xml_node_to_hash_with_libxml(result.root)}
    end 

    def xml_node_to_hash_with_libxml(node) 
      # If we are at the root of the document, start the hash 
      if node.element? 
        if node.children? 
          result_hash = {} 

          node.each_child do |child| 
            result = xml_node_to_hash_with_libxml(child) 

            if child.name == "text"
              if !child.next? and !child.prev?
                return result
              end
            elsif result_hash[child.name]
              if result_hash[child.name].is_a?(Object::Array)
                result_hash[child.name] << result
              else
                result_hash[child.name] = [result_hash[child.name]] << result
              end
            else 
              result_hash[child.name] = result
            end
          end
          return result_hash 
        else 
          # Nodes of sort <audio_languages/>, are arrays, 
          # and nodes like <average_rating "nil"="true"/> are nil values.
          if node.to_s.match(/^\<(.+)\/\>$/) && nil == node.attributes["nil"]
            return []
          end
          return nil 
        end 
      else 
        return node.content.to_s 
      end 
    end          
  end
end

How to convert XML to hash in Rails where empty array and nil values are preserved

1 Answers1