class TestSubject
    include Mongoid::Document

    embeds_one :response_body,
               class_name: "SerializedHash",
               as: :needs_hash,
               cascade_callbacks: true

    after_initialize :initialize_hash

    def initialize_hash
      self.response_body ||= SerializedHash.new
    end

  end

class SerializedHash
  include Mongoid::Document

  embedded_in :needs_hash, polymorphic: true
  field :serialized_hash, type: String, default: ""


  before_save :serialize_hash
  after_initialize :deserialize_hash

  attr_reader :hash_back
  delegate :[], :[]=, :size, :each, :to => :hash_back


  def deserialize_hash
    if serialized_hash && ! serialized_hash.empty?
      @hash_back = Marshal.load serialized_hash
    else
      @hash_back = {}
    end
  end

  def serialize_hash
    puts "before save"
    self.serialized_hash = Marshal.dump(@hash_back)
  end

end

  test "can serialize hash" do
    subject = TestSubject.create

    subject.response_body["a"] = 0
    subject.response_body["b"] = 1

    assert_equal({"a" => 0, "b" => 1}, subject.response_body.hash_back)
    sh = Marshal.dump subject.response_body.hash_back
    puts "saving!"
    subject.save

    assert_equal({"a" => 0, "b" => 1}, subject.response_body.hash_back)
    assert_equal sh, subject.response_body.serialized_hash
    subject.reload
    assert_equal({"a" => 0, "b" => 1}, subject.response_body.hash_back)
  end