How can I generate an ObjectId with mongoose?

Question

I'd like to generate a MongoDB ObjectId with Mongoose. Is there a way to access the ObjectId constructor from Mongoose?

• This question is about generating a new ObjectId from scratch. The generated ID is a brand new universally unique ID.

• Another question asks about creating an ObjectId from an existing string representation. In this case, you already have a string representation of an ID—it may or may not be universally unique—and you are parsing it into an ObjectId.

Solution 1

You can find the ObjectId constructor on require('mongoose').Types. Here is an example:

var mongoose = require('mongoose');
var id = mongoose.Types.ObjectId();

id is a newly generated ObjectId.

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Note: As Joshua Sherman points out, with Mongoose 6 you must prefix the call with new:

var id = new mongoose.Types.ObjectId();

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You can read more about the Types object at Mongoose#Types documentation.

Solution 2

You can create a new MongoDB ObjectId like this using mongoose:

var mongoose = require('mongoose');
var newId = new mongoose.mongo.ObjectId('56cb91bdc3464f14678934ca');
// or leave the id string blank to generate an id with a new hex identifier
var newId2 = new mongoose.mongo.ObjectId();

Solution 3

I needed to generate mongodb ids on client side.

After digging into the mongodb source code i found they generate ObjectIDs using npm bson lib.

If ever you need only to generate an ObjectID without installing the whole mongodb / mongoose package, you can import the lighter bson library :

const bson = require('bson');
new bson.ObjectId(); // 5cabe64dcf0d4447fa60f5e2

Note: There is also an npm project named bson-objectid being even lighter

Solution 4

With ES6 syntax

import mongoose from "mongoose";

// Generate a new new ObjectId
const newId2 = new mongoose.Types.ObjectId();
// Convert string to ObjectId
const newId = new mongoose.Types.ObjectId('56cb91bdc3464f14678934ca');

View more solutions

Comments

[R01010010]

how can you be sure that this is really unique? does mongoose any check before?

[Dmitry Minkovsky]

@R01010010 check out how these are generated (Google). There's no check but it's probabilistic

[Raja]

If you generate 16777216 within one second on the same machine, then you will probably get a duplicate. :)

[Evading Shadows]

Correction: If you generate 16777216 within one millisecond on the same machine, then you will probably get a duplicate. 😁

[Saahithyan Vigneswaran]

@joeytwiddle what is this number 16777216 ?

[Dmitry Minkovsky]

@SaahithyanVigneswaran it's 2^24, supposing you are using 24 bits for the random portion of the ID

[Raja]

How are MongoDB's ObjectIds generated? The local counter is three bytes, or six hex chars. We can calculate: 256 ** 3 === 16 ** 6 === 16777216

[Joshua Sherman]

looks like with mongoose 6 you have to add new new mongoose.Types.ObjectId()

[Dmitry Minkovsky]

Thank you @JoshuaSherman. I updated the answer.

[MartianMartian]

what's the diff between mongoose.Type and mongoose.Schema.Types ?

[stefano]

mongoose.Schema.Types will be used to within your schema when you want to reference between collections. To create a single objectId within your code use simply mongoose.Types