nested populate virtuals returning null

Hi Folks,

Continue to struggle with populating virtual fields nested in an array

#4278 #4262

'use strict';

//var mongoose = require('mongoose');
var Schema = mongoose.Schema;

//mongoose.connect('mongodb://localhost/test');

var options = {
  toObject: {getters: true},
  toJSON: {getters: true}
};

var BSchema = new Schema({
  name: String,
  c_id:  String
}, options);

BSchema.virtual('cs', {  // <-- comment this block in then the b_list array is null
  ref: 'C',
  localField: 'c_id',
  foreignField: 'fk_c_id'
});

var ASchema = new Schema({
  name: String,
  b_list: {
    type: [BSchema]
  }
}, options);

var CSchema = new Schema({
  name: String,
  fk_c_id: {type: String, ref: 'B'}
}, options);

var A = mongoose.model('A', ASchema);
var B = mongoose.model('B', BSchema);
var C = mongoose.model('C', CSchema);

A.find().populate({
  path: 'b_list',
  model: 'B',
  populate: {
    path: 'cs',
    model: 'C'
  }
}).exec().then(function (result) {
  console.log(JSON.stringify(result, null, 4));
});

return;

// to populate
var c = new C({name: 'C1', fk_c_id: 'c_id_1'});
c.save().then(function (c) {
  var b = new B({name: 'B1', c_id: 'c_id_1'});
  return b.save();
}).then(function (b) {
  var a = new A({name: 'A1', b_list: [ b ]});
  return a.save();
}).then(function () {
  A.find().populate({
    path: 'b_list',
    populate: {
      path: 'cs'
    }
  }).exec().then(function (result) {
    console.log(JSON.stringify(result, null, 4));
  });
}).catch(function (err) {
  return console.log(err.message);
});

Without BSchema.virtual(‘cs’, { …

> [
    {
        "_id": "57aa4870415890f84857e260",
        "name": "A1",
        "__v": 0,
        "b_list": [
            {
                "_id": "57aa4870415890f84857e25f",
                "c_id": "c_id_1",
                "name": "B1",
                "__v": 0,
                "id": "57aa4870415890f84857e25f"
            }
        ],
        "id": "57aa4870415890f84857e260"
    }
]

but when I attempt to populate b_list (array of B) and access the child cs I am getting nulls

 BSchema.virtual('cs', {  ...   

> [
    {
        "_id": "57aa4870415890f84857e260",
        "name": "A1",
        "__v": 0,
        "b_list": [
            null
        ],
        "id": "57aa4870415890f84857e260"
    }
]

I’m hoping this is something to do with my populate. Can someone suggest a fix or verify an issue?

To repro, comment in and out the BSchema.virtual(‘cs’, { …

Populate the first time by commenting in the the return; short circuit.

Thanks to you all!

[vkarpov15]

Perhaps because your user has an _fid field?

[svnindia]

The issue addressed with #4683