Mongoose getter function doesn't return updated array when making async calls

I have an app which makes use of two models: Movie and Tag. The idea is that one can create a record of a movie and attach tags to it. A Movie references one or more Tag models via the Movie.tags attribute which is a array containing the ObjectId of corresponding Tags.

When displaying the properties of a Movie on the client side it makes sense to display the text of the tag, rather than the ObjectId of the tag (remember: Movie.tags is an array of ObjectIds). I thought about the problem and concluded that the best method would be to make use of a getter function, so that when I retrieve a Movie document, the value of tags attribute is converted from an array of ObjectIds into an array of corresponding tag names.

To do this I must perform a db query for each ObjectId in the array Movie.tags. Since db queries are done asynchronously in Mongoose, I tried implementing the getter function using async.forEach() function from the Async module. The problem is that the final value is not being returned at the end of the async.forEach function.

I have two questions regarding this problem:

1. Given my overall objective, is using a getter function the best way of going about this?
2. Why is async.forEach() failing to return the updated array?

from model.js

/**
 * Mongo database models
 */

function defineModels(mongoose, async, fn) {
  var Schema = mongoose.Schema,
      ObjectId = Schema.ObjectId;

  /**
   * Model - Movie
   */

  /**
   * Getter function
   * 
   * Gets tag text as well as tag ObjectId.
   */
  function getTagNames(tags) {
    var newArray = new Array();
    async.forEach(
      tags,
      function(id, done) {
        mongoose.models['Tag'].findOne({ _id: id }, function(err, doc) {
          if (err) {
            done(err);
          }
          else if (doc) {
            newArray.push(doc);
            done(null);
          }
          else {
            console.log(doc);
            // Just incase something weird like no document is found.  
            // Technically this condition should not occur in reality. But we 
            // put something here to catch it just in case.
            done(new Error('No tag document found.'));
          }
        });
      },
      function(err) {
        if (err) {
          throw err;
        }
        console.log(newArray);
        return newArray;
      }
    );
  }

  /**
   * Define schema
   */
  Movie = new Schema({
    'name': String,
    'machineFileName': String,
    'originalFileName': String,
    'size': Number,
    'type': String,
    'permanent': { 
      type: Boolean, 
      default: false 
    },
    'dateUploaded': Date,
    'amountUploaded': {
      type: [], 
      default: 0 
    },
    'viewed': Number,
    'uid': String,
    'flags': [],
    'tags': {
      type: Array, 
      get: getTagNames
    }
  }, { strict: true });

  mongoose.model('Movie', Movie);

  /**
   * Model - Tag
   */
  Tag = new Schema({
    'title': { type: String, unique: true, sparse: true }
  }, { strict: true });

  mongoose.model('Tag', Tag);

  fn();
}

exports.defineModels = defineModels; 

Retrieving the document:

/**
 * View individual movie.
 */
exports.movie = function(req, res) {
  var Movie = mongoose.model('Movie');
  Movie.findById(req.params.id, function(err, doc) {
    if (err) {
      res.send('An error occured.', 500);
    }
    else {
      console.log('View movie');
      console.log(doc);
      res.render('movie', {
        locals: {
          title: 'Watch Movie',
          movie: doc
        }
      });
    }
  });
}