title: Mongoose: Populate a populated field
body: <p>I'm using MongoDB as a log keeper for my app to then sync mobile clients. I have this models set up in NodeJS:</p>
  
  <pre><code>var UserArticle = new Schema({
      date: { type: Number, default: Math.round((new Date()).getTime() / 1000) }, //Timestamp!
      user: [{type: Schema.ObjectId, ref: "User"}],
      article: [{type: Schema.ObjectId, ref: "Article"}],
      place: Number,    
      read: Number,     
      starred: Number,   
      source: String
  });
  mongoose.model("UserArticle",UserArticle);
  
  var Log = new Schema({
      user: [{type: Schema.ObjectId, ref: "User"}],
      action: Number, // O => Insert, 1 => Update, 2 => Delete
      uarticle: [{type: Schema.ObjectId, ref: "UserArticle"}],
      timestamp: { type: Number, default: Math.round((new Date()).getTime() / 1000) }
  });
  mongoose.model("Log",Log);</code></pre>
  
  <p>When I want to retrive the log I use the follwing code: </p>
  
  <pre><code>
  var log = mongoose.model('Log');
  log
  .where("user", req.session.user)
  .desc("timestamp")
  .populate("uarticle")
  .populate("uarticle.article")
  .run(function (err, articles) {
  if (err) {
      console.log(err);
          res.send(500);
      return;
  }
  res.json(articles);
  </code></pre>
  
  <p>As you can see, I want mongoose to populate the "uarticle" field from the Log collection and, then, I want to populate the "article" field of the UserArticle ("uarticle").</p>
  
  <p>But, using this code, Mongoose only populates "uarticle" using the UserArticle Model, but not the article field inside of uarticle.</p>
  
  <p>Is it possible to accomplish it using Mongoose and populate() or I should do something else?</p>
  
  <p>Thank you,</p>