How would you populate references nested in an object of an array using mongoose?

Question

How would you populate the product fields inside the cart array below?

{
    "_id": "5bbd1c6e2c48f512fcd733b4",
    "cart": [
        {
            "count": 1,
            "_id": "5bbd30ed9417363f345b15fc",
            "product": "5ba93a6d5d907d9512e43b75"
        }
        {
            "count": 2,
            "_id": "5bbd30ed9417363f345babcc",
            "product": "5ba93a6d5d2359512e43b75"
        }
        ],
    "totalItems": 0,
    "name": "kellie"
}

Schema is:

const usersSchema = new mongoose.Schema({
    cart: [
        {
            product: {type: mongoose.Schema.Types.ObjectId, ref: 'product'},
            count: {type: Number},
        },
    ],
    totalItems: {type: Number, default: 0},
    totalPrice: {type: Number},
});

I tried to research a solution with no luck.

Answer 1

I reproduced you schema (the main part with the cart.product ) and had no issues populating via the usual populate.exec() method:

var result = Author.findOne({ _id: "5bbd93a29fceda195bec8665" })
.populate("books.book")
.exec()
.then(result => {
  console.log(result)
})

My Author schema had same card.product thing but it is books.book :

var AuthorSchema = new Schema({
  books: [{
      book: { type: Schema.Types.ObjectId, ref: "Book" },
      count: {type: Number}
    }
  ]
}

Same happens with Author.find({}) etc.