I have seen folder named "helpers" inside api. I am not finding any document or example how to use helper. I had created one helper js "user-model.js" and I referring it as following in controller
var userDAO = require('../helpers/user-model.js');
I am looking for a way to include helper automatically in swagger.yaml. I want to put common functionality in helper and want to use it in project. I am not getting enough information how to use it.

I'm in the same situation. Hoping this project is still alive?

If it helps, since it is based of a127, this may apply:
apigee 127 docs Helper functions, I'm going to give it a shot.