MONKEY PATCH: no "xml type=yaml" in your .to_xml dump of activerecord objects

gistfile1.rb

# RAILS 2.3.15
#
# Since <tag type="yaml"> was removed from rails' xml parsing, 
# but not from its to_xml method, rails can't talk to an API 
# generated by rails, if you have serialized attributes.

# This can be put in config/initializers and you should probably 
# upgrade to rails 3 already. Ugh.

# Three parts:

# Part one:
#
# This makes it so that a hash to_xml doesn't have "<hash>" as
# the root element. This might break your app if you rely on
# this output like so:
# { :foo => "Bar" }.to_xml
# => <hash><foo>Bar</foo></hash>
# because this removes the "<hash>" and "</hash>" parts.
Hash::XML_FORMATTING['hash'] = Proc.new { |hash| hash.to_xml(:skip_instruct=>true, :root => "---fuck---").gsub(/\<\/?---fuck---\>\n/, "").html_safe }

# Part two: remove the "type=yaml" from your xml tag and make it 
# "type=hash" which probably breaks some spec somewhere
module ActiveRecord
  class XmlSerializer
    class Attribute
      def compute_type
        type = if @record.class.serialized_attributes.has_key?(name)
                # this is the only line changed from AR
                 @record.class.serialized_attributes[name].name.downcase.to_sym
               else
                 @record.class.columns_hash[name].try(:type)
               end
        case type
          when :text
            :string
          when :time
            :datetime
          else
            type
        end
      end
    end
  end
end

# part 3, when building xml we want to dump the xml right in there
# instead of escaping it.
module Builder
  class XmlBase < BlankSlate

    # this is all copied from xmlbase.rb in rails except for one line....
    def method_missing(sym, *args, &block)
      text = nil
      attrs = nil
      sym = "#{sym}:#{args.shift}" if args.first.kind_of?(Symbol)

      args.each do |arg|
        case arg
        when Hash
          attrs ||= {}
          attrs.merge!(arg)
        else
          text ||= ''
          text << arg.to_s
        end
      end
      if block
        unless text.nil?
          raise ArgumentError, "XmlMarkup cannot mix a text argument with a block"
        end
        _indent
        _start_tag(sym, attrs)
        _newline
        _nested_structures(block)
        _indent
        _end_tag(sym)
        _newline
      elsif text.nil?
        _indent
        _start_tag(sym, attrs, true)
        _newline
      else
        _indent
        _start_tag(sym, attrs)
        #
        # this line!
        #
        # if you have a hash that was serialized as xml already, don't escape it here.
        #
        if args.size > 0 && args[1][:type] == :hash
          _text text # don't escape
        else
          text! text
        end
        _end_tag(sym)
        _newline
      end
      @target
    end
  end
end

Thats some crazy shit, but so far the only solution I found, thanks for sharing!

seems to be coming for 3.0.20
https://github.com/rails/rails/pull/8853/files

FYI monkey-patch:

if Rails.version == "3.0.19"
  ActiveModel::Serializers::Xml::Serializer::Attribute.class_eval do
    def compute_type_with_nil
      return if value.nil?
      compute_type_without_nil
    end
    alias_method_chain :compute_type, :nil
  end
else
  raise "remove this #{__FILE__}"
end