as per Initialize max value in Ruby on Rails ActiveRecord, automagically

Initialize max value the Server Way in a Fat Model, the server way

class Item < ActiveRecord::Base
  validates_presence_of :display_order
  validates_uniqueness_of :display_order
...
def after_initialize
  if self.display_order.nil? then #if the section is new (created) and sequence order has no value
      if $item_display_order_max_value.nil? then    
         $item_display_order_max_value = Item.maximum('display_order')
         $item_display_order_max_value = 0 if item_display_order_max_value.nil?
         $item_display_order_max_value += 1
         self.display_order = $item_display_order_max_value
      else
        $item_display_order_max_value += 1
        self.display_order = $item_display_order_max_value
  end
end

as per http://www.falsepositives.com/index.php/2010/08/23/initialize-max-value-in-ruby-on-rails-activerecord-automagically/ Initialize max value in Ruby on Rails ActiveRecord, automagically