comments_controller.rb

def create
  unless @commentable.nil?
    @comment = @commentable.comments.create!(params[:comment])
    respond_to do |format|
      format.html { redirect_to @commentable }
      format.json { @commentable.to_json }
      format.partial { render :partial => "comments/comment.html.erb",
                              :object => @comment,
                              :layout => false }
    end
  end
end