gistfile1.txt

module WithAssociation
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def belongs_to(key, opts = {})
      column = "#{key}_id" #opts[:foreign_key] || "#{key}_id"
      id_writer = "#{column}=".to_sym
      id_reader = "#{column}".to_sym
      obj_reader = key
      obj_writer = "#{key}=".to_sym

      attr_key = key

      obj_class = opts[:class] || opts[:class_name].try(&:constantize) || key.to_s.camelcase.constantize

      define_method("attr_") do
        @attr_ ||= {}
      end
      
      define_method("attr_cached_") do
        @attr_cached_ ||= {}
      end

      define_method(obj_reader) do
        obj_id = self.attr_[attr_key]
        return nil if obj_id.nil?
        cached = self.attr_cached_[attr_key] 
        if cached.nil?
          cached = self.attr_cached_[attr_key] = obj_class.find(self.attr_[attr_key]) 
        end
        return cached
      end

      define_method(obj_writer) do |obj|
        if obj.nil?
          invalidate_cached_(attr_key)
          self.attr_.delete(attr_key)
        else
          self.attr_[attr_key] = obj.id
          self.attr_cached_[attr_key] = obj
        end
      end

      define_method(id_reader) do
        self.attr_[attr_key]
      end

      define_method(id_writer) do |obj|
        self.attr_[attr_key] = obj
        invalidate_cached_(attr_key)
      end

      define_method(:invalidate_cached_) do |key|
        self.attr_cached_.delete(key) if self.attr_cached_[key]
      end

      return nil
    end

    def associates_all(*args)
      keys.each { |key| associates(key) }
    end
  end
end