only return document _id on mongoose .find()

I update 100’s of documents every second by pushing new data to an array in its document. To get the document of which I am going to add data to, I use the mongoose .find().limit(1) function, and return the whole document. It works fine.

To help with some memory and cpu issues I have, I was wondering how I could get find() to only return the id of the document so I can use that to $push or $set new data.

Thanks.

Answer

You want to use Projection to tell your query exactly what you want off of your objects.

_id is always included unless you tell it not to.

readings = await collection
.find({
    name: "Some name you want"
})
.project({
    _id: 1 // By default
})
.toArray();