dirty_object.rb

require 'rubygems'
require 'dm-core'

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, 'sqlite3::memory:')

class Session
  include DataMapper::Resource

  property :id,   Serial
  property :data, Object, :lazy => false
end

DataMapper.auto_migrate!

SessionHash = Class.new(Hash)
session_data = SessionHash.new
session = Session.create(:data => session_data)

# Simply assign data to the object
session.data["flash"] = {:error => "I'm not dirty!"}
puts session.dirty? # would love to be true, but not required

# Reassign an edited object
session_data["flash"] = {:error => "I'm not dirty!"}
session.data = session_data
puts session.dirty? # why not dirty?!

# Reassign a dupped object
session.data = session_data.dup
puts session.dirty? # not even trying, are we?

# Clear, and reassign
session.data = nil
session.data = session_data
puts session.dirty? # well, that sux