change transactional primary key to custom ID for better portability

db/migrate/20170403155531_create_cashier_login_logs.rb

@@ -1,6 +1,8 @@
 class CreateCashierLoginLogs < ActiveRecord::Migration[5.0]
   def change
-    create_table :cashier_login_logs do |t|
+    create_table :cashier_login_logs, :id => false, :primary_key => :cashier_login_log_id do |t|
+      t.string :cashier_login_log_id, :limit => 16, :null => false, :index => true, :unique => true #custom primary key - to ensure consistence for cloud syncing
+
       t.references :cashier_terminal, foreign_key: true
       t.references :employee, foreign_key: true
       t.datetime :login_at, :null => false