Upsert ref documents when pushing to array in Express - arrays

Question

I have a Candidate schema with an array of refs to an Endorser schema. Like so:
const CandidateSchema = new mongoose.Schema({
name: {
type: String,
required: true,
trim: true
},
endorsements: [{
type: mongoose.Schema.Types.ObjectId,
ref: 'Endorser'
}]
});
const EndorserSchema = new mongoose.Schema({
name: {
type: String,
required: true,
trim: true
},
});
I receive endorsements in the form of an array of strings (i.e., the endorser's name). I want to iterate through that array and retrieve the _id of each from the Endorser model or upsert a new one if it doesn't exist. I then want to push those refs onto the existing candidate instance.
The following code works, but I really don't feel comfortable modifying the candidate instance in-memory. Having to do the promise resolution separately also seems weird.
const endorsementPromises = endorsements.map(async endorser => {
let endorserObj = await Endorser.findOneAndUpdate({name: endorser}, {name: endorser}, {upsert: true, new: true});
return endorserObj._id;
});
const endorsementArray = await Promise.all(endorsementPromises);
candidate.endorsements = candidate.endorsements.concat(endorsementArray);
await candidate.save();
I have tried using findOneAndUpdate with $push and $each. However, this only returns an error and doesn't update the document.
Candidate.update(
{id: candidate._id},
{$push: {
endorsements: {
$each: endorsementArray
}
}}
);
// the error
Error: {"n":0,"nModified":0,"ok":1}
I'm not sure why $push and $each aren't updating the document.
Any guidance would be really appreciated.

Answer 1

Try using $addToSet instead of $push. Also, it seems like you should be matching on _id instead of id in your update.