ObjectId and how it is generated in MongoDB

Introduction

An ObjectId is a unique ID used to identify documents in MongoDB. It helps find and organize data easily.

When you want to uniquely identify each record in a MongoDB collection.

When you need a timestamp to know when a document was created.

When you want a small, fast, and unique ID without extra setup.

When you want to avoid manually creating IDs for your data.

When you want to sort documents by creation time automatically.

Syntax

MongoDB

ObjectId()

ObjectId is a 12-byte unique identifier generated automatically by MongoDB.

It contains a timestamp, machine ID, process ID, and a counter to ensure uniqueness.

Examples

Creates a new unique ObjectId with the current timestamp.

MongoDB

new ObjectId()

Creates an ObjectId from a given 24-character hex string.

MongoDB

ObjectId("507f1f77bcf86cd799439011")

Sample Program

This inserts a document with name 'Alice' and then retrieves its ObjectId.

MongoDB

db.test.insertOne({name: "Alice"})
var doc = db.test.findOne({name: "Alice"})
doc._id

Important Notes

The first 4 bytes of ObjectId represent the creation timestamp in seconds.

ObjectId is unique across machines and processes, so no two documents get the same ID.

You can extract the creation time from an ObjectId using its timestamp.

Summary

ObjectId is a unique 12-byte ID automatically created by MongoDB.

It includes a timestamp, so you know when the document was made.

Use ObjectId to identify and sort documents easily without extra work.