title: Mongoose + Populate a property in a subdocument
body: <p>With mongoose, I want to populate a property inside a subdocument of my main document.
  Here is my models:</p>
  
  <pre><code>var device = {
      deviceId: {type: String, required: true},
      number: {type: Number, default: 0}
  };
  
  var notification = new Schema({
     createdAt: {type: Date, default: Date.now},
     device: {type: Schema.ObjectId, ref: 'Device'}
  });
  
  var clientSchema = new Schema({
      [...]
      information: {
          code: {type: String, required: true},
          name: {type: String, required: true}
      },
      notifications: [notification],
      [...]
  });
  </code></pre>
  
  <p>What I'm trying to do it's to get notifications with the device populated.</p>
  
  <p>I tried this:</p>
  
  <pre><code> clientModel.findOne({"information.code": id})
        .populate('notifications')
        .populate('notifications.device')
        .exec(function(err, client) {
            if (err) {
                console.log(err);
                next(err, null);
            }
            if (client) {
                console.log(client.notifications);
                next(null, client.notifications);
            }
        });
  </code></pre>
  
  <p>And I got this</p>
  
  <pre><code>[{ device: 55634975d20f1f3903ff4325,
     _id: 5564b1139ac484db0251b4a2,
     createdAt: Tue May 26 2015 19:44:51 GMT+0200 (CEST) }]
  </code></pre>
  
  <p>Anyone can tell me what I'm doing wrong please ??
  Thanks for your help guys :)</p>