conversions.rb

module ActiveSupport #:nodoc:
  module CoreExtensions #:nodoc:
    module Hash #:nodoc:
      module Conversions
        module ClassMethods
          def typecast_xml_value(value)
            case value.class.to_s
              when 'Hash'
                if value['type'] == 'array'
                  # If it has more than 2 keys tag has attributes
                  if value.keys.size != 2
                    value.delete('type')
                    typecast_xml_value(value)
                  else
                    child_key, entries = value.detect { |k,v| k != 'type' }   # child_key is throwaway
                    if entries.nil? || (c = value['__content__'] && c.blank?)
                      []
                    else
                      case entries.class.to_s   # something weird with classes not matching here.  maybe singleton methods breaking is_a?
                      when "Array"
                        entries.collect { |v| typecast_xml_value(v) }
                      when "Hash"
                        [typecast_xml_value(entries)]
                      else
                        raise "can't typecast #{entries.inspect}"
                      end
                    end
                  end
                elsif value.has_key?("__content__")
                  content = value["__content__"]
                  if parser = XML_PARSING[value["type"]]
                    if parser.arity == 2
                      XML_PARSING[value["type"]].call(content, value)
                    else
                      XML_PARSING[value["type"]].call(content)
                    end
                  else
                    content
                  end
                elsif value['type'] == 'string' && value['nil'] != 'true'
                  ""
                # blank or nil parsed values are represented by nil
                elsif value.blank? || value['nil'] == 'true'
                  nil
                # If the type is the only element which makes it then 
                # this still makes the value nil, except if type is
                # a XML node(where type['value'] is a Hash)
                elsif value['type'] && value.size == 1 && !value['type'].is_a?(::Hash)
                  nil
                else
                  xml_value = value.inject({}) do |h,(k,v)|
                    h[k] = typecast_xml_value(v)
                    h
                  end
                  
                  # Turn { :files => { :file => #<StringIO> } into { :files => #<StringIO> } so it is compatible with
                  # how multipart uploaded files from HTML appear
                  xml_value["file"].is_a?(StringIO) ? xml_value["file"] : xml_value
                end
              when 'Array'
                value.map! { |i| typecast_xml_value(i) }
                case value.length
                  when 0 then nil
                  when 1 then value.first
                  else value
                end
              when 'String'
                value
              else
                raise "can't typecast #{value.class.name} - #{value.inspect}"
            end
          end
        end
      end
    end
  end
end

example.rb

require 'active_support'
# Works like before
Hash.from_xml('
<projects type="array">
  <project>
    <name>project 1</name>
  </project>
  <project>
    <name>project 2</name>
  </project>
  <project>
    <name>project 3</name>
  </project>
</projects>
')
# => {"projects"=>[{"name"=>"project 1"}, {"name"=>"project 2"}, {"name"=>"project 3"}]}

# Works like before
Hash.from_xml('
<projects page="1" per_page="3">
  <project>
    <name>project 1</name>
  </project>
  <project>
    <name>project 2</name>
  </project>
  <project>
    <name>project 3</name>
  </project>
</projects>
')
# => {"projects"=>{"project"=>[{"name"=>"project 1"}, {"name"=>"project 2"}, {"name"=>"project 3"}], "per_page"=>"3", "page"=>"1"}}

# Modified behaviour: type="array" is ignored when other attributes are provided
# This behaviour doesn't break previous tests
Hash.from_xml('
<projects page="1" per_page="3" type="array">
  <project>
    <name>project 1</name>
  </project>
  <project>
    <name>project 2</name>
  </project>
  <project>
    <name>project 3</name>
  </project>
</projects>
')
# => {"projects"=>{"project"=>[{"name"=>"project 1"}, {"name"=>"project 2"}, {"name"=>"project 3"}], "per_page"=>"3", "page"=>"1"}}