articleSchema favoritecount

var mongoose = require('mongoose');
var uniqueValidator = require('mongoose-unique-validator');
var slug = require('slug'); // package for auto-creating URL slugs
var User = mongoose.model('User');

//...

// this is really slow for a large collection of users, but it gives an accurate result.
// iterate over all users and count how many have this article in their favorite list
ArticleSchema.methods.updateFavoriteCount = function() {
  var article = this;
  return User.count({favorites: {$in: [article._id]}}).then(function(count){
    article.favoritesCount = count;
    return article.save();
  });
};

mongoose.model('Article', ArticleSchema);