I'm afraid I don't yet follow your problem: what's hard about having a function listen for a change in the db, performing the business logic, and updating another value?
I need to segment the db into two sections: a section the client can update, and another section that only the protected business logic can update. It's doable, but more difficult than the traditional setup. Also when I started this project functions weren't available-- that happened in March of this year. Initially I used a machine elsewhere in my infrastructure to do this work of watching for the changes then writing to the restricted access areas.