Outrageous Ruby metaprogramming ಠ_ಠ. Also, quite fun

bios_controller.rb

require "dependency_loader"

class BiosController < ApplicationController
  extend DependencyLoader(:person)

  def new
    @bio = @person.bios.build
  end

  # ...
end

dependency_loader.rb

def DependencyLoader(name)
  Module.new do
    include DependencyLoader

    define_singleton_method :extended do |base|
      base.__load_dependency__ name
    end
  end
end

module DependencyLoader
  def __load_dependency__(name)
    loader = "load_#{name}"
    klass = name.to_s.classify.constantize
    ivar = "@#{name}"

    define_method loader do
      if instance_variable_get(ivar).nil?
        instance_variable_set ivar, klass.find(params["#{name}_id"])
      end
    end

    before_filter loader
  end
end