worlds simplest presenter pattern. drop in replacement for ActiveRecord/Mongoid models in your controller

presenter.rb

# the worlds lightest weight presenter pattern.  to use simply
#
# file app/presenters/post_presenter.rb
#
# PostPresenter =
#   Presenter.for(Post) do
#     validates_presence_of :custom_field_for_this_form
#
#   end
#
# works with ActiveRecord and Mongoid models
#
  begin
    require 'rails_helper'
  rescue LoadError
  end

class Presenter
  def Presenter.for(model, &block)
    Class.new(model).class_eval do
      presenter = self

      singleton_class = class << presenter; self; end

      singleton_class.module_eval do
        define_method(:model_name){ model.model_name }
      end

      if model.respond_to?(:table_name)
        presenter.set_table_name(model.table_name)
      end

      if model.respond_to?(:base_class)
        singleton_class.send(:define_method, :base_class){ model.base_class }
      end

      if model.respond_to?(:collection_name)
        presenter.collection_name = model.collection_name
      end

      if model.respond_to?(:hereditary?)
        singleton_class.send(:define_method, :hereditary?){ false }
        define_method(:hereditary?){ self.class.hereditary? }
      end

      define_method(:helper){ @helper ||= Helper.new } if defined?(Helper)

      presenter.class_eval(&block) if block

      presenter
    end
  end
end

Class.new() can take a block, so you don't need the class_eval().

You could also make use of Ruby 1.9's singleton_class() and define_singleton_method(), if you don't need to run on 1.8.

the block has to run after my setup, so i do need to run it manually.

I meant this:

Class.new(model).class_eval do

can be:

Class.new(model) do

Right?

oh @JEG2 - you're right. i'll right my fugly codez!

ps. i argued for years pre 'singleton_class' (vs metaclass). glad that turned out...