The Data APIs are not actually generated. The Data API service exposes a JSON query language on any Postgres table. So if you want to customise the controller,

The Data APIs are not actually generated. The Data API service exposes a JSON query language on any Postgres table. So if you want to customise the controller, the easiest thing to do is to write a custom API endpoint (which you can deploy to your server using a heroku style git-push or a docker image) which in turn can contact the data APIs or even the Postgres database directly.