# in works controller i want to change the action_required attribute
# of a related medium, depending on whether the checkbox value
# :action_required_done (no attribute, just a check_box_tag) is set

# params are [:work][:medium_attributes] from a nested form
# [:medium_attributes] has something called :action_required

  def update
    @work = Work.find(params[:id])

    respond_to do |format|
      # does what i want
      if params[:action_required_done]
        @work.medium.update_attribute(:action_required, false)
      end
      # alas this resets :action_required to the submitted data
      if @work.update_attributes(params[:work])

# how do i avoid the second update?