Mongodb How to update documents already found - node.js

Question

I'm building a movie rating system.
After entering the user ID, content ID, and rating registered in the rating document,
It was implemented by updating the rating in the content document.
How can I update the content document while I have already found it like the code below?
router.post('/', authenticate, async (req: IRequest<IRating>, res) => {
try {
const document = await Rating.create({
contentId: req.body.contentId,
contentType: req.body.contentType,
rating: req.body.rating,
review: req.body.review,
userId: req.user?._id,
});
const content = await Content.findOne({
type: req.body.contentType,
_id: document._id,
});
if (content) {
await content.updateOne(
{},
{
average: (content.average + document.rating) / content.count + 1,
count: content.count + 1,
},
);
}
res.json({ success: true, document, content });
} catch (err) {
res.status(404).json({ success: false, message: 'sever error' });
}
});

Answer 1

You can update with pipeline instead of use 2 queries, which for your current code can look like:
await Content.findOneAndUpdate(
{
type: req.body.contentType,
_id: document._id,
},
[{$set: {
average: {$divide: [{$add: ["$content.average", document.rating]},
{$add: ["$content.count", 1]}]},
count: {$add: ["$content.count", 1]}
}}])
But I don't think this is the right way to calculate an average. You should consider multiplying the existing $content.average by $content.count before adding the new document.rating