Mongoose — findOneAndUpdate() causing document duplication - node.js

Question

I'm using findOneAndUpdate() with upsert: true in order for a document to be updated if it exists and to be created otherwise. The tracks variable contains an array of Track instances. tracks does contain a few duplicates and that's where the problem begins. It causes the piece of code on line 7 (Observation.findOneAndUpdate(...)) to create a (low) number of duplicates, i.e. multiple documents that have the same (user, track) pair. Note that those duplicates are inserted randomly: running twice this piece of code brings different duplicated documents. My guess is that it has something to do with how the locking of data is done in MongoDB and that I'm doing too many operations at the same time. Any idea on how I could overcome this problem?
const promises = [];
​
tracks.forEach((track) => {
const query = { user, track };
const options = { new: true, upsert: true };
const newOb = { user, track, type: 'recent' };
promises.push(Observation.findOneAndUpdate(query, newOb, options));
});
​
return Promise.all(promises);
I'm using mongoose 5.5.8 and node 11.10.0.
Here's the Observation model:
const { Schema } = mongoose;
const ObservationSchema = new Schema({
track: { type: Schema.Types.ObjectId, ref: 'Track' },
user: { type: Schema.Types.ObjectId, ref: 'User' },
type: String
});
ObservationSchema.index({ track: 1, user: 1 }, { unique: true });
const Observation = mongoose.model('Observation', ObservationSchema);
And this is a sample of what the tracks array contains:
[
{ artists: [ 5da304b140185c5cb82d7eee ],
_id: 5da304b240185c5cb82d7f48,
spotifyId: '4QrEErhD78BjNFXpXDaTjH',
__v: 0,
isrc: 'DEF058230916',
name: 'Hungarian Dance No.17 In F Sharp Minor',
popularity: 25 },
{ artists: [ 5da304b140185c5cb82d7eee ],
_id: 5da304b240185c5cb82d7f5d,
spotifyId: '06dn1SnXsax9kJwMEpgBhD',
__v: 0,
isrc: 'DEF058230912',
name: 'Hungarian Dance No.13 In D',
popularity: 25 }
]
Thanks :)

Answer 1

I think this is due to your Promise.all method.
You should await every single query in the loop instead of awaiting everything at the same time at the end. Here an example with find:
async function retrieveApples() {
const apples = [];
arr.forEach(apple => {
const foundApple = await AppleModel.findOne({ apple });
apples.push(foundApple);
});
return apples
}