Mongoose and node.js, populating and saving in database?

Those are my two schematics for discussions and replies:

Source code for the two schematics

This is in my controller:

Source code for the controller

I am trying to get the logged in user and his reply (as string) and to save it in mongoose database, so I can show it under the current discussion.

That's how the database is right now:

"reply": [],

Any ideas how I can do this?

via shefasf