A population of virtual type in the nested path is not visible in toJSON.

[csy1204]

Prerequisites

• I have written a descriptive issue title

Mongoose version

7.0.2

Node.js version

v16.13.2

MongoDB version

4.4

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

11.3

Issue

I have an issue about toJSON in a nested virtual path.
As shown in the code below, I have populated the virtual type of the path in the multi-level and I see that the data of c1, c2 exists. But when I do the toJSON, I don't see that data.
{ toJSON: { virtuals: true } option also didn't work. I would like your help if you can solve this problem.

Example Code

const mongoose = require('mongoose');

const { Schema } = mongoose;

const TagsSchema = new Schema({
  codes: [String]
}, { toJSON: { virtuals: true }, toObject: { virtuals: true } });

const PostSchema = new Schema({
  name: String,
  tag: TagsSchema
}, { toJSON: { virtuals: true }, toObject: { virtuals: true } });

PostSchema.virtual('tag.cs', {
  ref: 'Test2',
  localField: 'tag.codes',
  foreignField: 'code'
});

const TagSchema = new Schema({
  code: String,
  url: String
});

const Post = db.model('Test1', PostSchema);
const Tag = db.model('Test2', TagSchema);

const c1 = await Tag.create({ code: 'c1', url: 'https://www.google.com' });
const c2 = await Tag.create({ code: 'c2', url: 'https://www.google.com' });
const c3 = await Tag.create({ code: 'c3', url: 'https://www.google.com' });

const b1 = await Post.create({ name: 'b1', tag: { codes: ['c1', 'c2'] } });
const b2 = await Post.create({ name: 'b2', tag: { codes: ['c2'] } });
const b3 = await Post.create({ name: 'b3', tag: { codes: ['c3'] } });

// Pouplate the nested virtual path
const Bs = await Post.find().populate('tag.cs').exec();

console.log(Bs[0].tag.cs); // [c1, c2] is printed
// [
//   {
//     _id: '641823432714c10f648c056b',
//     code: 'c1',
//     url: 'https://www.google.com',
//     __v: 0
//   },
//   {
//     _id: '641823452714c10f648c056d',
//     code: 'c2',
//     url: 'https://www.google.com',
//     __v: 0
//   }
// ]
console.log(Bs[0].toJSON().tag.cs); // undefined -> c1, c2 is expected
console.log(Bs[0].tag.toJSON().cs); // undefined -> c1, c2 is expected

[csy1204]

mongoose/lib/virtualtype.js

Lines 140 to 145 in f490627

	VirtualType.prototype.applyGetters = function(value, doc) {
	if (utils.hasUserDefinedProperty(this.options, ['ref', 'refPath']) &&
	doc.$$populatedVirtuals &&
	doc.$$populatedVirtuals.hasOwnProperty(this.path)) {
	value = doc.$$populatedVirtuals[this.path];
	}

I think the problem is that doc.$$populatedVirtuals is undefined - for whatever reason, $$populatedVirtuals was not created.