title: Mongoose Populate not working
body: <p>Hello i have this Schema(called schema.js):</p>
  
  <pre><code>var mongoose = require('mongoose'),
  Schema = mongoose.Schema;
  
  var RoomSchema = new Schema({
    name: { type: String, required: true, index: { unique: true } },
    people: { type: Number, required: true },
    childrens: {type: Number, required: true},
    total: {type: Number, required: true}
  });
  
  var Room = mongoose.model('Room', RoomSchema);
  
  var AvSchema = new Schema({
    roomId:  {type: Schema.Types.ObjectId, ref: 'Room'},
    people: { type: Number, required: true },
    childrens: {type: Number, required: true},
    total: {type: Number, required: true}
  });
  
  var Av = mongoose.model('Av', AvSchema);
  
  module.exports = {
    Room: Room,
    Av: Av
  };
  </code></pre>
  
  <p>in my Route file : </p>
  
  <pre><code>module.exports = function(app) {
    var model = require('../models/Schema');
  
    app.get('/api/rooms', function(req, res) {
      model.Room.find(function(err, rooms) {
        if (err)
          res.send(err);
  
        res.json(rooms);
      });
    });
  
  
    app.get('/api/av', function(req, res) {
      model.Av.find().populate('roomId').exec(function(err, av) {
        if (err)
          res.send(err);
  
        res.json(av);
      });
    });
  };
  </code></pre>
  
  <p>A pic of the db :
  <img src="https://i.stack.imgur.com/dKALo.png" alt="enter image description here"></p>
  
  <p>GET /api/rooms - response:</p>
  
  <pre><code>[{
    "_id": "5444d0dd9a31437167eea816",
    "name": "Single",
    "people": 1,
    "childrens": 1,
    "total": 4
  }, {
    "_id": "5444d1009a31437167eea817",
    "name": "Double",
    "people": 2,
    "childrens": 2,
    "total": 10
  }]
  </code></pre>
  
  <p>When i call api/rooms looks fine but when i call api/av i got an empty array [] .... Any idea what i do wrong? I should mention that i have inserted records in av collection for both roomsID</p>
  
  <p>Thank you in advance.</p>