change transactional primary key to custom ID for better portability

db/migrate/20170414090001_create_assigned_order_items.rb

@@ -1,9 +1,10 @@
 class CreateAssignedOrderItems < ActiveRecord::Migration[5.0]
   def change
-    create_table :assigned_order_items do |t|
+    create_table :assigned_order_items, :id => false, :primary_key => :assigned_order_item_id do |t|
+      t.string :assigned_order_item_id, :limit => 16, :null => false, :index => true, :unique => true #custom primary key - to ensure consistence for cloud syncing
       t.string     :item_code, :null => false, :index => true
       t.references :order_queue_station, foreign_key: true
-      t.references :order, foreign_key: true
+      t.string :order_id, foreign_key: true, :limit => 16
       t.boolean :print_status
       t.boolean :delivery_status