Updating timestamp when adding model via association

What's the proper way to update a models timestamp when you add an
object to one of it's associations?

For example, if I have a model, Business, that has_many :addresses,
when I add a new Address, I'd like the updated_at timestamp for the
business object to get updated.

Doing:

@business.addresses.create(....)

Does not update the updated_at timestamp for @business. What's the
best way to get it to update?

Thank you,
Kenny

If you're using Rails 2.1 and have ActiveRecord::Base.partial_updates
= true, you can try this:

class Address
  belongs_to :business
  before_save :update_business
  private
    def update_business
      if self.business && self.business_id_changed?
        self.business.updated_at = Time.now
      end
end