🍁 MongoDB — Lesson 1: Intro & Setup

Traditional relational databases (MySQL, PostgreSQL) store data in structured tables with fixed schemas. MongoDB takes a fundamentally different approach — data lives in documents inside collections.

Document

A document is a JSON-like object (stored as BSON internally). It is the basic unit of data in MongoDB, equivalent to a row in SQL — but far more flexible.

// A MongoDB document — a user record
{
  "_id": ObjectId("64a1b2c3d4e5f60718293a4b"),
  "name": "Alice Johnson",
  "email": "alice@example.com",
  "age": 29,
  "active": true,
  "tags": ["admin", "editor"],
  "address": {
    "city": "New York",
    "zip": "10001"
  },
  "createdAt": ISODate("2024-01-15T09:30:00Z")
}

Collection

A collection is a group of documents — like a SQL table, but without an enforced schema. Documents in the same collection can have different fields.

Database

A MongoDB server can host multiple databases. Each database has its own collections. Common databases: myapp, test, admin, local.

_id field

Every document must have a unique _id field. If you don't provide one, MongoDB auto-generates an ObjectId — a 12-byte BSON type that encodes timestamp + machine + process + counter. This guarantees global uniqueness without a central authority.

// ObjectId structure (12 bytes)
ObjectId("64a1b2c3  d4e5  f607  182  93a4b")
//        ^------^ ^--^ ^--^ ^--^ ^---^
//        4b time  3b   2b   1b   3b
//                 mac  pid  inc  counter

// Extract the timestamp from an ObjectId:
ObjectId("64a1b2c3d4e5f60718293a4b").getTimestamp()
// ISODate("2023-07-02T12:00:00Z")

BSON (Binary JSON)

MongoDB stores documents as BSON — a binary-encoded format that extends JSON with additional types:

Ubuntu / Debian (apt)

# Import MongoDB public GPG key
curl -fsSL https://pgp.mongodb.com/server-7.0.asc | \
  sudo gpg -o /usr/share/keyrings/mongodb-server-7.0.gpg --dearmor

# Add MongoDB repository
echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] \
  https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | \
  sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list

# Install MongoDB
sudo apt-get update
sudo apt-get install -y mongodb-org

# Start and enable the service
sudo systemctl start mongod
sudo systemctl enable mongod

# Verify it's running
sudo systemctl status mongod

macOS (Homebrew)

# Tap the MongoDB formula repository
brew tap mongodb/brew

# Install MongoDB Community Edition
brew install mongodb-community@7.0

# Start MongoDB as a background service
brew services start mongodb-community@7.0

# Or run it manually (foreground)
mongod --config /usr/local/etc/mongod.conf

Windows (MSI Installer)

# 1. Download the MSI from:
#    https://www.mongodb.com/try/download/community
#    Select: Version 7.0, Platform: Windows, Package: msi

# 2. Run the installer
#    - Choose "Complete" installation
#    - Check "Install MongoDB as a Service"
#    - Default data path: C:\data\db
#    - Default log path:  C:\data\log\mongod.log

# 3. mongod is now in: C:\Program Files\MongoDB\Server\7.0\bin\
# 4. Add it to your PATH environment variable

# 5. Start the service (if not auto-started)
net start MongoDB

# 6. Stop the service
net stop MongoDB

Install mongosh (MongoDB Shell)

# Ubuntu
sudo apt-get install -y mongosh

# macOS
brew install mongosh

# Windows — download from:
# https://www.mongodb.com/try/download/shell

# Or via npm (all platforms)
npm install -g mongosh

# Connect to local MongoDB (default port 27017)
mongosh

# Connect to a specific host and port
mongosh "mongodb://localhost:27017"

# Connect with authentication
mongosh "mongodb://username:password@localhost:27017/mydb"

# Connect to MongoDB Atlas
mongosh "mongodb+srv://user:pass@cluster0.abcde.mongodb.net/mydb"

Shell Navigation Commands

// Show all databases
show dbs

// Switch to (or create) a database
use myapp

// Show current database name
db

// Show all collections in current database
show collections

// Show all users in current database
show users

// Drop the current database
db.dropDatabase()

// Get database stats
db.stats()

// Get collection stats
db.users.stats()

// Show server status
db.serverStatus()

MongoDB Atlas is the fully managed cloud database service. The free tier (M0) gives you 512MB of storage — perfect for learning and small projects.

Setup Steps

1. Go to cloud.mongodb.com and create a free account
2. Create a new Organization and Project
3. Click "Build a Database" → Select M0 Free
4. Choose a cloud provider (AWS / GCP / Azure) and region closest to you
5. Name your cluster (e.g., Cluster0)
6. Create a Database User with username + password
7. Add your IP to the IP Access List (or use 0.0.0.0/0 for any IP)
8. Click "Connect" → "Connect with MongoDB Shell" to get your URI

# Your Atlas connection string looks like:
mongosh "mongodb+srv://myUser:myPassword@cluster0.abcde.mongodb.net/"

# Store it as an environment variable (never hardcode passwords)
export MONGODB_URI="mongodb+srv://myUser:myPassword@cluster0.abcde.mongodb.net/"
mongosh "$MONGODB_URI"

Insert and Query

// Switch to a new database (created lazily on first write)
use learnmongo

// Insert a single document into the "users" collection
db.users.insertOne({
  name: "Bob Smith",
  email: "bob@example.com",
  age: 32,
  skills: ["JavaScript", "Python"],
  joinedAt: new Date()
})

// Output:
// {
//   acknowledged: true,
//   insertedId: ObjectId("64a1b2c3d4e5f60718293a4b")
// }

// Insert multiple documents at once
db.users.insertMany([
  { name: "Carol White", email: "carol@example.com", age: 25 },
  { name: "Dave Brown", email: "dave@example.com", age: 41 }
])

// Find ALL documents in the collection
db.users.find()

// Find with a filter (age greater than 30)
db.users.find({ age: { $gt: 30 } })

// Find ONE document by email
db.users.findOne({ email: "bob@example.com" })

// Find and project only name and email (hide _id)
db.users.find({}, { name: 1, email: 1, _id: 0 })

Count and Sort

// Count all documents
db.users.countDocuments()

// Count with a filter
db.users.countDocuments({ age: { $gte: 30 } })

// Sort by age ascending (1) or descending (-1)
db.users.find().sort({ age: 1 })
db.users.find().sort({ age: -1 })

// Chain: filter + sort + limit + skip
db.users.find({ active: true })
        .sort({ name: 1 })
        .skip(10)
        .limit(5)

// Step 1: Start the shell and create a database
use bookstore

// Step 2: Insert some books
db.books.insertMany([
  {
    title: "The Pragmatic Programmer",
    author: "Andrew Hunt",
    year: 1999,
    price: 49.99,
    tags: ["programming", "software"],
    inStock: true
  },
  {
    title: "Clean Code",
    author: "Robert C. Martin",
    year: 2008,
    price: 39.99,
    tags: ["programming", "best practices"],
    inStock: true
  },
  {
    title: "Designing Data-Intensive Applications",
    author: "Martin Kleppmann",
    year: 2017,
    price: 59.99,
    tags: ["databases", "distributed systems"],
    inStock: false
  }
])

// Step 3: Find books in stock
db.books.find({ inStock: true })

// Step 4: Find books under $50, sorted by year
db.books.find({ price: { $lt: 50 } }).sort({ year: 1 })

// Step 5: Count books with "programming" tag
db.books.countDocuments({ tags: "programming" })

// Step 6: Show only title and price
db.books.find({}, { title: 1, price: 1, _id: 0 })