Mongodb $lookup/populate and summarize - node.js

Question

I'm trying to join two schema and summarize the total price.
This is the schema:
const Product = new mongoose.Schema({
name: { type: String, required: true },
price: Number
})
const Order = new mongoose.Schema({
fullname: { type: String, required: true },
address: { type: String, required: true },
products: [
{
product: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Product',
},
quantity: Number,
},
],
})
I want to create aggregation to get orders with total price.so it could be like:
[
{
fullname: 'jhon doe',
address: 'NY 1030',
products: [
{
product: {
name: 'Piano',
price: 50
},
quantity: 10,
},
],
price: 500
}
]
I try to use aggregation framework without any success, any idea?

Answer 1

Updated
As the question needs the price to be calculated by sum of the multiplication of quantity and product price, It can be done with below code:
db.getCollection('orders').aggregate([
{ $unwind: { path: '$products' } },
{
$lookup: {
from: 'products',
localField: 'products.product',
foreignField: '_id',
as: 'p',
},
},
{ $unwind: { path: '$p' } },
{
$group: {
_id: '$_id',
price: { $sum: { $multiply: ['$p.price', '$products.quantity'] } },
fullname: { $first: '$fullname' },
address: { $first: '$address' },
products: { $push: { product: '$p', quantity: '$products.quantity' } },
},
},
])
----------------------------------------------------------------------------------------------------------------------------
You can use $lookup in aggregation as below:
db.getCollection('orders').aggregate([
{
$lookup: {
from: 'products',
localField: 'products.product',
foreignField: '_id',
as: 'p',
},
},
{ $unwind: { path: '$p' } },
{
$project: {
fullname: 1,
address: 1,
products: {
product: '$p',
quantity: 1,
},
price: 1,
},
},
])