How to read database table in Application.rb

I am adding CORS validation in application.rb filw where domain names are given in Environment variable but I want to keep all domain in database table and validate these domain during CORS validation. I am unable to read database table in application.rb file. Could you please help me how I can implement this. Please find the below summary of this requirement.

1. Add domain name in Database table
2. Application will validate Domain whether requested domain is already existing in database or not , it would be first step because if domain is not registered in DB then won't allow

Thanks for your help. I need some inputs on this asap.