comments_controller.rb

# Example of nested resource with CanCan
class CommentsController < ApplicationController
  before_filter :load_and_authorize_resource

  # ...
  
  protected
  
  def load_resource
    @article = Article.find(params[:article_id])
    unless params[:action] == "index"
      if params[:id]
        @comment = @article.comments.find(params[:id])
      else
        @comment = @article.comments.build(params[:talk])
      end
    end
  end
end