Using cookies in a model

Well, let's say I have an Article class. What I would like is being
able to define a method like that :

def rated?
    if cookies["rate-article-#{self.id.to_s}"] == "rated"
      true
    else
      false
    end
end

So that I can use it in my views to check if the current user has
rated this article or not.

BUT the "cookies" method isn't defined for ActiveRecord::Base
I tryied to include many modules (ActionController::Cookies ,
ActionController::Helper, ...) and cannot succeed.

Any help is welcome.

Thanks,

Florent J.