change transactional primary key to custom ID for better portability

db/migrate/20170403135121_create_customers.rb

@@ -1,6 +1,7 @@
 class CreateCustomers < ActiveRecord::Migration[5.0]
   def change
-    create_table :customers do |t|
+    create_table :customers, :id => false, :primary_key => :customer_id do |t|
+      t.string :customer_id, :limit => 16, :null => false, :index => true, :unique => true #custom foreign_key to prevent conflict during sync
       t.string :name, :null => false
       t.string :company
       t.string :contact_no