dirty_block_approach.rb

module Imageable
  def self.build(methods)
    mod = Module.new do
      methods.each do |method|
        define_method method do
          images.find { |image| image.kind == 'main_image' }
        end
      end
    end

    mod.define_singleton_method :included do |model_class|
      model_class.has_many :images
    end

    mod
  end
end