The document is updated only once. Mongoose - node.js

Question

I'm finding document by _id from array. Then I change the field 'balance' and save the document. This action is performed five times, but the balance is changed only once. Code:
users.forEach(async(user) => {
if (user.active) {
/* SOME STUFF */
const owner = await Owner.findById(user.owner)
owner.balance = (owner.balance * 100 - 0.01 * 100) / 100
await owner.save()
}
})
Tried like that:
Owner.findById(user.owner).then((owner) => {
owner.balance = (owner.balance * 100 - 0.01 * 100) / 100
owner.save(err => {
if(err) console.log(err)
})
})
Also tried:
owner.markModified(balance);
Owner schema:
const ownerSchema = new Schema({
balance: {
type: Number
}
});
Test output from console
On this picture you can see test output. Balance before is 99.53.
As a result, the balance should be 99.48, but it is 99.52.

Answer 1

You might be expecting that each user would be processed one by one inside forEach(), but this is not what would happen, everything would rather run simultaneously.
What you would need to do for your code to run in order is to use for...of instead, which would ensure execution order. Something like below:
for(let user of users) {
if (user.active) {
/* SOME STUFF */
const owner = await Owner.findById(user.owner)
owner.balance = (owner.balance * 100 - 0.01 * 100) / 100
await owner.save()
}
}

Answer 2

why don't you try something like
Owner.findByIdAndUpdate()
it will find owner by id & update it it is shortened and better (clean) version of your code

Answer 3

The problem lies in your use of the forEach function.
when you write async in-front of a function you basically wrap it as a promise meaning its return value is changed to be a promise.
forEach does not have a return value, meaning when you wrap it as a promise no-one is waiting for that promise, that leads to unexpected behaviour. and in your case it actually does update 5 times, but not synchronicity as you expect.
i recommend using a library like bluebird as it gives alot of power, the code would look like this:
let Promise = require("bluebird")
....
let users = [user array];
await Promise.mapSeries(users, (user) => {
if (user.active) {
/* SOME STUFF */
const owner = await Owner.findById(user.owner)
owner.balance = (owner.balance * 100 - 0.01 * 100) / 100
await owner.save()
}
})
it will now work as you want.