serializers.rb

class NativeSerializer
  def encode
    value.inspect
  end

  def decode(value)
    eval(value)
  end
end

class JSONSerializer
  def initialize
    @encoder = Yajl::Encoder
    @decoder = Yajl::Parser
  end

  def encode(value)
    @encoder.encode(value)
  end

  def decode(value)
    @decoder.parse(value)
  end
end

module Serializable
  def self.extended(klass)
    klass.class_eval do
      @@serializers = {}
      
      def self.serializers
        @@serializers
      end
      
      def after_initialize
        @serialized = {}
        @serialized_changed = {}
      end
      
    private
      def perform_serialization
        @serialized.each do |key, value|
          if @serialized_changed[key]
            self[key] = @@serializers[key].encode(value)
          end
        end
      end
      before_save :perform_serialization
    end
  end

  def serialize_property(property, options = {})
    options[:serializer] ||= NativeSerializer.new
    serializers[property] = options[:serializer]
    
    define_method property do
      if @serialized[property].nil? && !self[property].nil?
        @serialized[property] = self.class.serializers[property].decode(self[property])
        @serialized_changed[property] = options[:autosave] ? true : false
      end

      @serialized[property]
    end

    define_method "#{property}=" do |value|
      @serialized[property] = value
      send("#{property}_changed!".to_sym)
    end

    define_method "#{property}_changed!" do
      @serialized_changed[property] = true
    end
  end
end

class Post < ActiveRecord::Base
  extend Serializable
  serialize_property :tags, :serializer => JSONSerializer.new
end