如何在保留空数组和nil值的Rails中将XML转换为哈希

Question

当我在Rails中将XML结构转换为使用Hash.from_xml(@xml)进行散列时，解析器不会区分空数组和nil值，而XML将立即以\终止的节点描述为空数组，例如<audio_languages/>与那些将属性nil="true"解释为nil值的节点。

XML结构(由我控制如何生成)如下所示：

<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>

Hash.from_xml(@xml)的预期输出为：

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

相反，对于audio_languages和avg_rating，我得到的值是空值

{"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}]}}}  

Answer 1

最后，我使用libxml解析节点，并检查节点是否具有所需的签名，以确定是否要转换为空数组或nil值。

# 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