Single database for multiple shops

Use ActsAsTenant as Multi-tenancy for shops

See below files:
- app/controllers/concern/multi_tenancy.rb
- app/models/application_record.rb
- app/models/shop.rb

An initializer can be created to control option in ActsAsTenant.
config/initializers/acts_as_tenant.rb
require 'acts_as_tenant/sidekiq'
ActsAsTenant.configure do |config|
  config.require_tenant = false # true
end

more details: https://github.com/ErwinM/acts_as_tenant

app/controllers/api/call_waiters_controller.rb

@@ -23,7 +23,7 @@ class Api::CallWaitersController < ActionController::API
     end 
     ActionCable.server.broadcast "call_waiter_channel",table: @table,time:@time,from: from, shift_ids: shift_ids 
     # get printer info
-    @shop          = Shop.first 
+    @shop          = Shop.current_shop 
     unique_code    = "CallWaiterPdf" 
     print_settings = PrintSetting.find_by_unique_code(unique_code)
     printer        = Printer::ReceiptPrinter.new(print_settings)