mongoose divide two fields in put request - node.js

Question

Can I update a field of a document with a division of two fields? Using Node and MongoDB, I'm trying to create a rating function, and I have to make a division, but nothing seems to work. I want the new value of rating to be, the current one divided by the number of votes.
router.put("/:id/:rating", async (req, res) => {
const movie_rating = parseInt(req.params.rating);
try {
const updatedMovie = await Movie.findByIdAndUpdate(
req.params.id,
{
$inc: { noVotes: 1 },
$inc: { rating: movie_rating },
$divide: { rating: [rating, noVotes] },
// rating: { $divide: [rating, noVotes] }
},
{ new: true }
);
res.status(200).json(updatedMovie);
} catch (err) {
res.status(500).json(err);
}
});

Answer 1

You need to change few things
Sample
db.collection.update({},
[
{
"$set": {
"key2": {
$add: [
"$key2",
1
]
},
key3: {
"$divide": [
{
$add: [
"$key2",
1
]
},
"$key"
]
},
}
}
],
{
"multi": true,
"upsert": false
})
You need aggregate update as you need divide
You cannot use the updated value in the same operation
You cannot combine $inc, $set in aggregate update
Alternatively, you can use $add instead $inc
you can reperform the operation for the divide operation than making another update call

Answer 2

This can be done with $set,
It will look like this:
router.put("/:id/:rating", async (req, res) => {
const movie_rating = parseInt(req.params.rating);
try {
const updatedMovie = await Movie.findByIdAndUpdate(
req.params.id,
[
{
$set: {
noVotes: { $sum: ["$noVotes", 1] },
rating: { $sum: ["$rating", movie_rating] },
averageRating: { $divide: ["$rating", "$noVotes"] },
},
},
],
{ new: true }
);
res.status(200).json(updatedMovie);
} catch (err) {
res.status(500).json(err);
}
});