gistfile1.rb

class LineItemObserver < ActiveRecord::Observer
  def before_save record
    current_date = record.order.start
    reservations = record.product.reservations

    while current_date < record.order.end
      reservation = reservations.where(:day => current_date).first

      if reservation.nil?
        reservations.create :quantity => record.quantity, :day => current_date
      else
        reservation.update_attributes :quantity => reservation.quantity + record.quantity
      end

      current_date += 1.day
    end
  end
end