push function to subdocument of a subdocument

Question

I'm working on a create order function for a shopping app that needs to group products into bags separated by provider, and I'm running into an issue where I have to push products into a model that looks like this:

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const schema = new Schema({
    userId: {type: String},
    status: {type: String, default: 'Pending'},
    bags:[
        {
            providerId: {type: String},
            products: [
                {
                    productId: {type: String},
                    quantity: {type: Number},
                    name: {type: String}
                }
            ]
        }
    ]
});

module.exports = mongoose.model('Order', schema);
Copy

This is the model of the cart from where I am getting the data:

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const schema = new Schema({
    userId: {type: String},
    products: [
        {
            productId: {type: String},
            providerId: {type: String},
            quantity: {type: Number},
            name: {type: String},
            price: {type: Number}
        }
    ],
});

module.exports = mongoose.model('Cart', schema);
Copy

This is the code that looks for the cart of the user and for each product tries to find an existing bag of the provider. If there's a bag, it dumps the product in there. Otherwise, it should create a new bag for that provider.

        let cart = await Cart.findOne({userId: userId});

        if(cart){

            let products = cart.products;
            let order = new Order;

            order.userId = userId;

            products.forEach(async (item) => {

                productId = item.productId;
                providerId = item.providerId;
                quantity = item.quantity;
                name = item.name;

                let itemIndex = order.bags.findIndex(p => p.providerId == providerId);

                if (itemIndex > -1) {

                    let existingBag = order.bags[itemIndex];
                    existingBag.products.push({ productId, quantity, name });

                }   else {

                    let newBag = order.bags;
                    newBag.providerId = providerId;
                    newBag.products.push({ productId, quantity, name });

                }
            })
Copy

With this code, I get the following error:

C:\\git\\ecooff-back\\orders\\order.service.js:71
newBag.products.push({ productId, quantity, name });
^

TypeError: Cannot read properties of undefined (reading 'push')
Copy

I've also tried order.bags.products.push() but I get the same error. I'm not sure how to deal with this double document nesting I got here.

I tried creating an instance of order.bags like this:

let newBag = new order.bags
Copy

But of course order.bags is not a constructor. Is there any way to create that constructor?

I'm using async on forEach, which I've read that could be conflicting, I'm not sure if that is a part of the problem too.

Any advice will be greatly appreciated!