rescue not being triggered

gistfile1.rb

  def set_category
    if current_user
      @category = current_user.categories.find(params[:id])
      begin
      rescue ActiveRecord::RecordNotFound
        flash[:error] = "The category you're looking for could not be found."
        redirect_to root_path
      end
    else
      flash[:error] = 'You must be logged in to do that'
      redirect_to root_path
    end

  end