user.controller.js

exports.show = function (req, res, next) {
  var username = req.params.username;

  var query = User.where({ username: username });
  query.findOne(function (err, user) {
    if (err) return next(err);
    if (!user) return res.send(401);
    res.json(user.profile); // this is where the magic happens
  });
};

user.model.js

var UserSchema = new Schema({
  username: String,
  role: {
    type: String,
    default: 'user'
  },
});

UserSchema
  .virtual('profile')
  .get(function() {
    return {
      'username': this.username,
      'role': this.role
    };
  });