Simplified Persistence Separation

gistfile1.rb

class MyApp::Post

  attr_reader :record

  def initialize(args)
    @record = args[:record]
  end

  def comment(attributes)
    create_comment(attributes)
  end

  def create_comment(attributes)
    comment_record = record.build_comment(attributes)
    comment = Comment.new(comment_record)
    
    self.add_comment?(comment)
    comment.add_post?(self)
    
    return comment_record
  end

  def add_comment?(comment)
    true
  end
end

class MyApp::Comment

  attr_reader :record

  def initialize(args)
    @record = args[:record]
  end

  def add_post?(post)
    true
  end
end

# controller.rb

def create
  @post = Post.find(1)

  @comment = comment(post, attributes)

  if @comment.save
    redirect @post
  else
    render :new
  end
end

def comment(post_record, comment_attributes)
  post = MyPost::Post.new(post_record)
  post.comment(attributes)
end

Review: http://en.wikipedia.org/wiki/Visitor_pattern