Question

Apologies in advance – I’m very much a learner, and writing projects as a means to learn. In this one, I’m trying to extend ActiveRecord so that I can do the following…

In my model definition, call …

attr_special :field, :field

Then, elsewhere, be able to access this list through something like

Model.special_attributes

Probably something really obvious. I’m fine extending ActiveRecord, but I’m not even sure what I’m searching for for guidance beyond this (constructor?)…

Answer 1

You can define something like the code below to create custom DSL in your models:

module SpecialAttributes
  module ClassMethods
    def attr_special(*attrs)
      class_attribute :special_attributes
      self.special_attributes = attrs
    end

    def special_attributes
      self.special_attributes
    end
  end

  module InstanceMethods
    # some code here
  end

  def self.included(base)
    base.extend ClassMethods
    base.send :include, InstanceMethods
  end

end

class ActiveRecord::Base
  include SpecialAttributes
end

I reopen ActiveRecord::Base class instead of use inheritance because it’s more common in Ruby that inheritance.

I like to use submodules called ClassMethods and InstanceMethods in my module and use self.included method to add them in the base class. So you can use ‘include MyModule’ without have to know if you add instance or class methods.

I hope I can help you.