How to get an aggregated result from mongoose subdocument when query parent?

I'm trying to build some advanced hello world app on top of express and mongoose. Assume I have next Schemas:

const pollOptionsSchema = new Schema({
  name: String,
  votes: {
    type: Number,
    default: 0
  }
});

const pollSchema = new Schema({
  name: String,
  dateCreated: { type: Date, default: Date.now },
  author: { type: Schema.Types.ObjectId },
  options: [pollOptionsSchema]
});

And when I simply call

Poll.findOne({_id: req.params.id}).exec((err, data) => {
  if (err) console.log(err);
  // I receive next data:
  // { _id: 58ef3d2c526ced15688bd1ea,
  //   name: 'Question',
  //   author: 58dcdadfaea29624982e2fc6,
  //   __v: 0,
  //   options:
  //    [ { name: 'stack', _id: 58ef3d2c526ced15688bd1ec, votes: 5 },
  //      { name: 'overflow', _id: 58ef3d2c526ced15688bd1eb, votes: 3 } ],
  //   dateCreated: 2017-04-13T08:56:12.044Z }
});

The question is how I could receive same data + aggregated number of votes (i.e 8 in case above) after calling some method on Model level, for example:

  // I want to receive:
  // { _id: 58ef3d2c526ced15688bd1ea,
  //   name: 'Question',
  //   author: 58dcdadfaea29624982e2fc6,
  //   __v: 0,
  //   totalNumberOfVotes: 8,
  //   options:
  //    [ { name: 'stack', _id: 58ef3d2c526ced15688bd1ec, votes: 5 },
  //      { name: 'overflow', _id: 58ef3d2c526ced15688bd1eb, votes: 3 } ],
  //   dateCreated: 2017-04-13T08:56:12.044Z }

Or maybe I need to implement some extra method on document level i.e (data.aggregate)?

I've already reviewed:

1. http://mongoosejs.com/docs/api.html#model_Model.mapReduce
2. http://mongoosejs.com/docs/api.html#aggregate_Aggregate
3. https://docs.mongodb.com/manual/core/map-reduce/
4. https://docs.mongodb.com/manual/tutorial/map-reduce-examples/

But can't utilize it for my case :(

Any advice will be much appreciated. Thanks!

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