Rails: updating an association

Question

I have a Reservation model which belongs_to a Sharedorder and so a Sharedorder has_many reservations.

Give you a little background.

I sharedorder has many reservations and each reservation can have an amount. A sharedorder has three status: 1) reserved, 2) confirmed, 3) and purchased.

Here is my problem. When a reservation gets added to a sharedorder or an existing reservation's amount is updated I need this to affect the associated sharedoder because the status listed latter should only change when 100% of the reservations have been placed and so on.

Here are the things I have tried: .

 class Reservation < ActiveRecord::Base
    before_save :sharedorder_reserved_status

  def sharedorder_reserved_status
  if self.sharedorder.reserved_percent(reservations_to_be_added) >= 100 && !self.sharedorder.reserved
  self.sharedorder.update_attribute(:reserved, true)
  self.sharedorder.update_attribute(:reserved_at, Time.now)
  end
 end

  def reservations_to_be_added
  if self.new_record? 
   self.amount 
   elsif self.amount_changed?
   self.amount - self.amount_was
   else
   0
  end  
 end
end

And then in the Sharedorder model:

class Sharedorder < ActiveRecord::Base
def reserved_percent(amount_change)
 (((reserved_sum + amount_change).to_f / self.product.twenty_hq_size.to_f)*100).to_i
end

 def reserved_sum 
  if !@reserved_sum
   reserved_sum = 0
   reserved_reservations.collect {|x| reserved_sum += x.amount }
   reserved_sum
   else
    @reserved_sum
   end
end


   def reserved_reservations
    @reserved_reservations ||= Reservation.find(:all, :conditions => ['canceled = ? AND sharedorder_id = ?', false, self.id ])
   end
  end

I have also tried :touch => true on the reservation model to update the sharedorder put for some reason it doesn't seem to include the latest reservation being added or being updated.

So what I'm trying to do is update the status of the sharedorder if a certain percent is reached and I have to send the additional amounts the the sharedorder for it to know to include additional reservations or updates on existing ones.

How should I do this?