Get random filtered values in mongoose (nodejs)

I'm writing a simple app to keep a list of questions to generate random exams. I defined this schemas:

Question schema:

var questionSchema = mongoose.Schema({
  text: String,
  type: {
    type: String,
    enum: ['multichoice', 'numerical', 'truefalse']
  },
  meta: {
    votes: {
      type: Number,
      default: 0
    },
    tags: [{
      type: mongoose.Schema.Types.ObjectId,
      ref: 'tag'
    }]
  }
});

Tag schema:

var tagSchema = mongoose.Schema({
  name: {
    type: String,
    unique: true
  }
});

What I'm trying to do is to get random questions (I'm using mongoose-random) filtering by tags, and here is the problem. My get route receive a list of comma separated tag names. How can I filter questions regarding if they contain that tag name? At the moment questions only have a list of tag ids and I don't see a way to do this.

At this moment this is the code used to fetch random questions:

Question.findRandom().limit(req.query.maxquestions).exec(function (err, questions) {
    if (err) {
        res.send(err);
    } else {
        res.set('Content-Type', 'text/json');
        res.json(questions);
    }
});

EDIT: This is my actual code to solve the problem

router.get('/exam', function(req, res) {
  var tags = req.query.tags.split(",");
  var tagsIds;
  var tagsProcessed = 0;

  var eventEmitter = new events.EventEmitter();
  eventEmitter.on('tagProcessed', function() {
    tagsProcessed++;

    if (tagsProcessed >= tags.length) {
      switch (req.query.format) {
        case "json":
        case "xml":
          break;
        case "html":
        default:
          if (req.isAuthenticated()) {
            console.log(tagsIds);
            Question.findRandom({'meta.$.tags': {$in: tagsIds}}).limit(req.query.questions).exec(function (err, questions) {
              if (err) {
                res.send(err);
              } else {
                res.set('Content-Type', 'text/html');
                res.render('exam', {
                  title: 'Smarty',
                  user: req.user,
                  questions: questions,

                });
              }
            });
          } else {
            res.redirect('/');
          }
      }
    }
  });

  if (tags.length > 0) {

    for (var i = 0; i < tags.length; i++) {
      Tag.find({name: tags[i]}, function(err, tag) {
        tagsIds.push(tag);
        eventEmitter.emit('tagProcessed');
      });
    }
  } else {
    eventEmitter.emit('tagProcessed');
  }
});

I tried to change the filter to:

Question.findRandom({'meta.$.tags': {$in: tagsIds}}).limit(req.query.questions).exec(function (err, questions) {

but I get the same result, an error that only shows {} (no message).

EDIT 2: There was a problem in my list of tag ids. I also changed the filter to {'meta.tags': { $in: tagsIds }} and now works but I have a little problem. If I had a question with tags foo and bar and I send a get request with tag foo, this question is not returned. How can I fix this?

EDIT 3: I was saving bad values. The solution proposed (with the filter modification) works.