MongoDB Introduction

What Is MongoDB?

MongoDB is an open-source NoSQL document database. It stores each record as a document—a JSON-like object that can hold nested fields and arrays—instead of a row in a fixed table.

Hierarchy:
  database → collection → document → field

Storage:  BSON (binary JSON)
Query:    find(), update methods, aggregation — not SQL

Documents live in collections; collections live in a database. This page is the gateway to the MongoDB tutorial—deeper topics have their own pages.

Why Use MongoDB?

MongoDB was built for large web apps where rigid tables slowed change and scale. The name comes from “humongous.”

How MongoDB Organizes Data

Each level contains many of the next. Keep this hierarchy in mind.

Cheat sheet — tools

What Does a Document Look Like?

One document from a users collection:

{
  _id: ObjectId("66f1c2a9e4b0a1b2c3d4e5f6"),
  name: "Asha Rao",
  email: "[email protected]",
  age: 29,
  address: { city: "Chennai", country: "India" },
  skills: ["JavaScript", "MongoDB"],
  createdAt: ISODate("2026-01-15T09:30:00Z")
}

Documents in one collection can differ, but real apps still follow a consistent shape. You can enforce one with schema validation. Max document size is 16 MB.

MongoDB vs SQL

If you know MySQL or PostgreSQL, map the ideas like this:

Same query, two styles

Users older than 25 — name and email, sorted by name:

SELECT name, email
FROM users
WHERE age > 25
ORDER BY name;

db.users.find(
  { age: { $gt: 25 } },
  { name: 1, email: 1, _id: 0 }
).sort({ name: 1 })

In find(), the first argument is the filter (WHERE) and the second picks fields (SELECT).

When to choose which

Your First MongoDB Commands

Insert one document and read it back in mongosh. MongoDB creates the database and collection on the first insert.

use school

db.students.insertOne({ name: "Ravi", grade: 8, subjects: ["Math", "Science"] })

db.students.find({ grade: 8 })

switched to db school
{
  acknowledged: true,
  insertedId: ObjectId('66f1c3b0e4b0a1b2c3d4e5f7')
}
[
  {
    _id: ObjectId('66f1c3b0e4b0a1b2c3d4e5f7'),
    name: 'Ravi',
    grade: 8,
    subjects: [ 'Math', 'Science' ]
  }
]

How It Works

1. Switch database. use school selects (or creates) the database.

2. Insert. insertOne adds one document to the students collection.

3. Query. find({ grade: 8 }) returns matching documents.

To run this yourself, follow the MongoDB installation guide. Updates and deletes are covered in CRUD operations.

Where Is MongoDB Used?

Common workloads where the document model fits well:

What Should You Learn Next?

Follow this path. Each topic has its own tutorial page.

Key Takeaways