Mongoose - How to prevent mongoose from creating _id on model instantiation - node.js

Question

I want MongoDB itself to add an _id upon insertion so I can track the insertion time using the ObjectID but when I do new MyModel(...), moongose will add the id field.
How do I prevent this so the db itself adds the id?
Alternatively how do I create a field which will be set to the INSERTION time by the db?
Edit: I see that this is not technically possible with mongoose, so would it be possible to add a field that is set by MongoDB when the insertion is done?
My model (if relevant):
{
timestamp: {
type: Date,
required: true
},
signaler: {
type: String,
required: true,
trim: true
},
source: {
type: String,
required: false,
trim: true
},
category: {
type: String,
required: false,
trim: true
},
key: {
type: String,
required: true,
trim: true
},
level: {
type: String,
required: false,
trim: true,
uppercase: true,
enum: ['ALARM', 'WARNING', 'NORMAL']
},
payload: {
type: Schema.Types.Mixed,
required: true
}
}

Answer 1

It's an interesting use case you have. Mongoose really does create that _id on when you call a Model constructor!
I see three paths forward:
Don't use mongoose. The lower level mongo driver doesn't create _ids util you insert into a collection.
Pass around a plain javascript object until you are ready to save
it, then use the Model.create method.
Finally, you can use the pre save middleware to update the _id, by manually generating a new one (with mongoose.Types.ObjectId()) that will have more accurate time info.
If you want to introduce a createdAt field that is updated when the document is inserted, then you are also going handle the pre save middleware. That's the way this popular plugin does it: https://github.com/drudge/mongoose-timestamp/blob/master/index.js