manager.rb

class Manager < ActiveRecord::Base
  belongs_to :demo
  
  serialize :state
  serialize :cache
  
  def after_initialize
    @observers = []
  end
  
  def kind
    read_attribute(:kind) or write_attribute(:kind, "example")
  end
  
  def before_save    
    logger.info "BEFORE SAVE: state = #{read_attribute(:state).to_yaml}"
    logger.info "BEFORE SAVE: cache = #{read_attribute(:cache).to_yaml}"
    logger.info "setting state to #{state.to_yaml}"
    write_attribute(:state, state)
    logger.info "setting state to #{cache.to_yaml}"
    write_attribute(:cache, cache)
  end
  
  def after_save
    logger.info "AFTER SAVE: state = #{read_attribute(:state).to_yaml}"
    logger.info "AFTER SAVE: cache = #{read_attribute(:cache).to_yaml}"
  end
  
  def object
    @object ||= new_object
  end
  
  def state
    object.state
  end
  
  def cache
    object.cache
  end
  
  def completed?(command)
    case command
    when :rollout
      object.position == object.tasks.length
    when :rollback
      object.position == 0
    end
  end
  
  def rollout
    object.rollout!
  end

  def rollback
    object.rollback!
  end
  
  def add_observer( obj )
    @observers << obj
    object.add_observer( obj )
  end
  
  def observed_by?( obj )
    @observers.include? obj
  end
  
  def task_count
    object.tasks.length
  end
  
  def method_missing(meth, *args)
    if object.respond_to?(meth)
      object.send(meth, *args)
    else
      super(meth, *args)
    end
  end
  
  private
  
  def new_object
    require File.join(RAILS_ROOT, 'lib', 'outback', "#{kind}.rb")
    
    @object = Outback.const_get(kind.camelize).create
    
    logger.info "Restoring state:" +
      {'state' => read_attribute(:state), 'cache' => read_attribute(:cache)}.to_yaml

    @object.restore_state(read_attribute(:state) || {:direction => 1, :position => 0})
    @object.cache = (read_attribute(:cache) || {})
          
    @object
  end
end

session.irb

Loading development environment (Rails 2.1.0)
>> m = Manager.new
=> #<Manager id: nil, state: nil, cache: nil, kind: nil, demo_id: nil, created_at: nil, updated_at: nil>
>> m.cache
Restoring state:--- 
cache: 
state: 

=> {}
>> m.cache[:name] = "Mike"
=> "Mike"
>> m.save
BEFORE SAVE: state = --- 

BEFORE SAVE: cache = --- 

setting state to --- 
:direction: 1
:position: 0

setting state to --- 
:name: Mike

  Manager Create (0.000565)   INSERT INTO "managers" ("updated_at", "cache", "kind", "demo_id", "state", "created_at") VALUES('2008-07-24 22:37:28', '--- 
:name: Mike
', 'example', NULL, '--- 
:direction: 1
:position: 0
', '2008-07-24 22:37:28')
AFTER SAVE: state = --- 
:direction: 1
:position: 0

AFTER SAVE: cache = --- 
:name: Mike

=> true
>> m
=> #<Manager id: 16, state: {:direction=>1, :position=>0}, cache: {:name=>"Mike"}, kind: "example", demo_id: nil, created_at: "2008-07-24 22:37:28", updated_at: "2008-07-24 22:37:28">
>> m = Manager.find(16)
  Manager Load (0.000491)   SELECT * FROM "managers" WHERE ("managers"."id" = 16) 
=> #<Manager id: 16, state: {:direction=>1, :position=>0}, cache: {:name=>"Mike"}, kind: "example", demo_id: nil, created_at: "2008-07-24 22:37:28", updated_at: "2008-07-24 22:37:28">
>> m.cache
Restoring state:--- 
cache: 
  :name: Mike
state: 
  :direction: 1
  :position: 0

=> {:name=>"Mike"}
>> m.cache[:name] = "John"
=> "John"
>> m.save
BEFORE SAVE: state = --- 
:direction: 1
:position: 0

BEFORE SAVE: cache = --- 
:name: John

setting state to --- 
:direction: 1
:position: 0

setting state to --- 
:name: John

AFTER SAVE: state = --- 
:direction: 1
:position: 0

AFTER SAVE: cache = --- 
:name: John

=> true
>> m = Manager.find(16)
  Manager Load (0.000880)   SELECT * FROM "managers" WHERE ("managers"."id" = 16) 
=> #<Manager id: 16, state: {:direction=>1, :position=>0}, cache: {:name=>"Mike"}, kind: "example", demo_id: nil, created_at: "2008-07-24 22:37:28", updated_at: "2008-07-24 22:37:28">