Stop 07 · NoSQL DatabasesTopics · 2/12

MongoDB Basics

In short

MongoDB is one of the most popular document databases, and it stores JSON-like objects, the same shape your Node code already uses. Very little translation needed.

The most popular document database — stores JSON-like documents in flexible collections instead of rigid tables, popular for rapid iteration and unstructured data.

The blob opens a steel almirah full of colourful folders and pulls out a fat file.

Think of it like this

The office almirah

A steel almirah (database) has shelves (collections), and each shelf holds files (documents). One student's file has three pages, another's has ten, with different forms inside. You never redesign the almirah to add a new kind of page.

Watch it happen

Database, collection, document

db: college

coll: students

coll: courses

doc: Riya

doc: Aman+hostel

doc: DBMS

1/5A MongoDB server holds databases. This app uses one called college.

The big ideas

What you need to know

Database, collection, document

The three levels. Roughly database, table, row, except documents in one collection can differ in shape.

BSON under the hood

Documents are stored as BSON, a binary JSON with extra types like ObjectId and Date.

_id on every document

MongoDB adds a unique ObjectId if you don't supply one. It even encodes when the id was created.

mongosh and drivers

Explore data with the mongosh shell. From Node, use the official mongodb driver or Mongoose.

See it in code

Walk through the code

1import { MongoClient } from "mongodb";2 3const client = new MongoClient("mongodb://localhost:27017");4await client.connect();5 6const students = client.db("college").collection("students");7 8await students.insertOne({ name: "Riya", year: 2 });9await students.insertOne({ name: "Aman", year: 3, hostel: "B-block" });10 11const found = await students.findOne({ name: "Aman" });12console.log(found?._id, found?.hostel);

1/4Connect to a local MongoDB on its default port, 27017.

Start MongoDB with docker run -p 27017:27017 mongo, then run this file as an ES module.

Save yourself the pain

Common mistakes

Oops

Expecting a typo in a field name to throw an error.

Do this instead

MongoDB happily stores 'naem'. Validate input in your app or use a schema tool like Mongoose.

Oops

Dumping every kind of record into one giant collection.

Do this instead

Keep documents of the same kind in their own collection, just as you'd make separate tables.

Your mission

First steps in mongosh

~15 min

Quick check

You insert a document into a collection that doesn't exist yet. What happens?

Go deeper

1Install MongoDB locally or use MongoDB Atlas's free tier.
2Practice basic CRUD operations using the `mongosh` shell.
3Compare a MongoDB document to the equivalent normalized SQL tables.