Turning extension of ActiveRecord in gem - ruby-on-rails

Question

This extension create cache_find method for all models of app (I've create this using this post).
config/active_record_extension.rb
require 'active_support/concern'
module ActiveRecordExtension
extend ActiveSupport::Concern
# add your instance methods here
def flush_find
Rails.cache.delete([self.class.name, :cached_find, id])
end
included do
after_commit :flush_find
end
module ClassMethods
def cached_find id
Rails.cache.fetch([self.name, :cached_find, id]) { self.find(id) }
end
end
end
# include the extension
ActiveRecord::Base.send(:include, ActiveRecordExtension)
I turned this code into a gem and added to this repo.
So I want to add this methods dynamically, something like this:
class User << ActiveRecord::Base
# id, name, email, age...
cached :find, :find_by_name, :find_by_email
end
and the above code should generate cached_find, flush_find, cached_find_by_name, flush_find_by_name... You get it.
I need help to:
Test Rails.cache methods in model_caching gem.
Create code to dynamically add methods to app models based on cached method arguments.
Some links that helped me but do not meet all:
https://github.com/radar/guides/blob/master/extending-active-record.md
http://railscasts.com/episodes/245-new-gem-with-bundler
http://guides.rubyonrails.org/plugins.html
Fell free to clone and improve gem code.

Answer 1

You don't have to hack ActiveRecord::Base. You can add what Marc-Alexandre said right into your concern, like so:
module ActiveRecordExtension
extend ActiveSupport::Concern
...
module ClassMethods
def cached(*args)
define_method "cached_#{arg.to_s}" do
# do whatever you want to do inside cached_xx
end
define_method "flush_#{arg.to_s}" do
# do whatever you want to to inside flush_xx
end
end
end
end
Also, I would not auto include the extension directly in ActiveRecord, I think it's better to explicitly include it in the models you are going to use it.

Answer 2

To add code dynamically you need to hack the ActiveRecord::Base class. In another file (you usually put in lib/core_ext) you could do as follow :
ActiveRecord::Base.class_eval do
def self.cached(*args)
args.each do |arg|
define_method "cached_#{arg.to_s}" do
# do whatever you want to do inside cached_xx
end
define_method "flush_#{arg.to_s}" do
# do whatever you want to to inside flush_xx
end
end
end
end
What it does basically is takes all your arguments for cached (:find, :find_by_name, etc) and define the two methods (cache_find, cache_find_by_name) and flush_find, .. etc)
Hope this helps !