Mongoose findbyIdAndUpdate - how to update one field using sum from another array field - node.js

Question

So this is how my document looks like
"donator": [
{
"_id": "5edbd7d182af1f5aceab62bb",
"donatorName": "Niki",
"donationValue": 5000000
},
{
"_id": "5edbd7d182af1f5aceab62bc",
"donatorName": "Brian",
"donationValue": 5000000
}
],
"currentValue" : 1000000
I get my currentValue from donationValue sum in donator array :
donator.reduce((a, { donationValue }) => a + donationValue,0);
and I want to update the document by adding new object in donator array, and automatically updates currentValue field when the data updated.
I tried using aggregate
MyCollection.findByIdAndUpdate(id, [
{
$set: req.body,
$set: { currentValue: { $sum: { $sum: donator.donationValue } } },
},
]);

Answer 1

It's a good practice to sanitise your input and not directly use req.body.
so let's say
const donator = sanitizeDonator(req.body)
Then you can add donator and update currentValue as follows.
Note that _id on donator won't be auto generated by the update query, so it has to be present in the donator object.
MyCollection.findByIdAndUpdate(id, [
{
$set: {
donator: {
$concatArrays: ["$donator", [donator]] // adding donator to the last element
}
}
}, {
$set: {
currentValue: {
$reduce: {
initialValue: 0,
input: "$donator",
in: {
$add: ["$$this.donationValue", "$$value"]
}
}
}
}
}
]);
Relevant APIs
$concatArrays,
$reduce