change transactional primary key to custom ID for better portability

db/migrate/20170414110918_create_booking_orders.rb

@@ -1,8 +1,10 @@
 class CreateBookingOrders < ActiveRecord::Migration[5.0]
   def change
-    create_table :booking_orders do |t|
-      t.references :booking, foreign_key: true
-      t.references :order, foreign_key: true
+    create_table :booking_orders, :id => false, :primary_key => :booking_order_id do |t|
+      t.string :booking_order_id, :limit => 16, :null => false, :index => true, :unique => true #custom primary key - to ensure consistence for cloud syncing
+
+      t.string :booking, foreign_key: true, :limit => 16
+      t.string :order, foreign_key: true, :limit => 16
 
       t.timestamps
     end