Populate an array of Model objects with mongoose

Question

This is the schema that I use. As you can see survey_codes model path consists of an Array of ObjectIds.

...
var Schema = mongoose.Schema;
var Email = mongoose.SchemaTypes.Email;
var ObjectId = mongoose.SchemaTypes.ObjectId;

var RestaurantSchema = new Schema({
  id                    : {type: String, required: true, unique: true},
  name                  : {type: String, required: true},
  owner_name            : String,
  reservation_email     : Email,
  survey_url            : String,
  survey_codes          : [{type: ObjectId, ref: SurveyCode}],
  created_at            : {type: Date, default: Date.now}
});

var SurveyCodeSchema = new Schema({
  code                  : {type: String, unique: true, required: true},
  valid                 : {type: Boolean, default: true},
  create_date           : {type: Date, default: Date.now},
  used_date             : {type: Date, default: null}
});

And here the function i'm trying to use:

Restaurant
    .findOne({ id: self.param('id') })
    .populate('survey_codes')
    .exec(function(err, restaurant) {
      if (err)
        console.log('Error in view survey codes function');
      if (!restaurant || restaurant.survey_codes.length < 1)
        self.res.send('No survey codes are yet generated.');
      else
        self.res.send(restaurant.survey_codes);
    });

When I'm executing the function, it gives me this error:

Locomotive 0.3.7 application starting in development on http://0.0.0.0:3000

/home/pblondin/nodejs-dev/rezerve-locomotive/node_modules/mongoose/lib/utils.js:419
        throw err;
              ^
MissingSchemaError: Schema hasn't been registered for model "function model(doc, fields, skipId) {
    if (!(this instanceof model))
      return new model(doc, fields, skipId);
    Model.call(this, doc, fields, skipId);
  }".

I just can't get my head over this one. This is the first time that I post here, and I've noticed couple of you guys answer to similar questions, but the solution is not working in my case.

Thanks!

EDITED:

Here is some additional info:

1) A sample from Restaurants collection:

[
    {
        "__v": 1,
        "_id": "52617861b9ee6c171b000001",
        "id": "AAA",
        "name": "Name",
        "owner_name": "Owner",
        "reservation_email": "email@new.com",
        "survey_url": "new@new.com",
        "created_at": "2013-10-18T18:05:21.447Z",
        "survey_codes": [
            "52617864b9ee6c171b000002",
            "52617864b9ee6c171b000003",
            "52617864b9ee6c171b000004",
            "52617864b9ee6c171b000005",
            "52617864b9ee6c171b000006",
            "52617864b9ee6c171b000007",
            "52617864b9ee6c171b000008",
            "52617864b9ee6c171b000009",
            "52617864b9ee6c171b00000a",
            "52617864b9ee6c171b00000b"
        ]
    }
]

2) Version of dependencies:

mongoose: 3.6.20
mongodb: 1.3.19
locomotive: 0.3.7
locomotive-mongoose: 0.1.0

Answer 1

SOLVED(!)

A simple typo in my model:

survey_codes          : [{type: ObjectId, ref: SurveyCode}],

ref as to be a model name, so 'SurveyCode' instead!