1. MongoDB Setup – CRUD Operations समझे (Beginner Guide) 2026

{
  "_id": ObjectId("65f1a2b3c4d5e6f7g8h9i0j1"),
  "name": "Vivek Sharma",
  "email": "vivek@example.com",
  "age": 25,
  "address": {
    "city": "Mumbai",
    "pincode": 400001
  },
  "hobbies": ["coding", "reading", "gaming"],
  "createdAt": ISODate("2026-01-15T10:30:00Z")
}

┌─────────────────────────────────────┐
│            USERS TABLE             │
├─────┬───────────┬──────────────────┤
│ id  │ name      │ email            │
├─────┼───────────┼──────────────────┤
│ 1   │ Vivek     │ vivek@test.com   │
│ 2   │ Deepti    │ deepti@test.com  │
└─────┴───────────┴──────────────────┘

- Fixed schema (columns fixed)
- Data related across tables (JOINs)
- ACID transactions

// Collection: users
[
  { "_id": 1, "name": "Vivek", "email": "vivek@test.com" },
  { "_id": 2, "name": "Deepti", "email": "deepti@test.com", "phone": "1234567890" }
]

- Flexible schema (fields can vary)
- Embedded documents (no JOINs needed)
- High scalability

# Import MongoDB public key
wget -qO - https://www.mongodb.org/static/pgp/server-6.0.asc | sudo apt-key add -

# Add MongoDB repository
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu $(lsb_release -cs)/mongodb-org/6.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-6.0.list

# Update and install
sudo apt update
sudo apt install -y mongodb-org

# Start MongoDB service
sudo systemctl start mongod
sudo systemctl enable mongod

# Check status
sudo systemctl status mongod

# Start MongoDB shell
mongosh

Connection String: mongodb://localhost:27017
Or Atlas: mongodb+srv://username:password@cluster.mongodb.net/

# Start shell
mongosh

# Connect to specific database
mongosh mongodb://localhost:27017/mydb

# With Atlas
mongosh "mongodb+srv://cluster.mongodb.net/mydb" --username myuser

// Show all databases
show dbs

// Switch to/create database
use mydb

// Show current database
db

// Show all collections
show collections

// Get database stats
db.stats()

// Drop current database
db.dropDatabase()

// General help
help

// Database methods help
db.help()

// Collection methods help
db.users.help()

// List all databases
show dbs

// Create/switch to database
use shopDB

// Check current database
db

// Get database stats
db.stats()
// Output: { "db": "shopDB", "collections": 0, "objects": 0, ... }

// Drop database (WARNING: deletes everything!)
db.dropDatabase()

// Create collection explicitly
db.createCollection("products")

// Create collection by inserting (auto-created)
db.users.insertOne({ name: "Vivek" })

// List collections
show collections
// or
db.getCollectionNames()

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

// Drop collection
db.products.drop()

// Insert one document
db.users.insertOne({
  name: "Vivek Sharma",
  email: "vivek@example.com",
  age: 25,
  city: "Mumbai"
})

// Output:
{
  acknowledged: true,
  insertedId: ObjectId("65f1a2b3c4d5e6f7g8h9i0j1")
}

// Insert multiple documents
db.users.insertMany([
  {
    name: "Priya Patel",
    email: "priya@example.com",
    age: 23,
    city: "Delhi"
  },
  {
    name: "Amit Kumar",
    email: "amit@example.com",
    age: 28,
    city: "Bangalore"
  },
  {
    name: "Neha Gupta",
    email: "neha@example.com",
    age: 26,
    city: "Mumbai"
  }
])

// Output:
{
  acknowledged: true,
  insertedIds: {
    '0': ObjectId("..."),
    '1': ObjectId("..."),
    '2': ObjectId("...")
  }
}

db.products.insertOne({
  name: "MacBook Pro",
  price: 150000,
  inStock: true,
  tags: ["electronics", "apple", "laptop"],
  specifications: {
    ram: "16GB",
    storage: "512GB",
    processor: "M3"
  },
  createdAt: new Date()
})

// Find all documents
db.users.find()

// Format output (pretty print)
db.users.find().pretty()

// Find with filter
db.users.find({ city: "Mumbai" })

// Find with multiple conditions
db.users.find({ city: "Mumbai", age: { $gt: 20 } })

// Find first matching document
db.users.findOne({ name: "Vivek Sharma" })

// Find by _id
db.users.findOne({ _id: ObjectId("65f1a2b3c4d5e6f7g8h9i0j1") })

// Comparison operators
db.users.find({ age: { $gt: 25 } })   // Greater than
db.users.find({ age: { $gte: 25 } })  // Greater than or equal
db.users.find({ age: { $lt: 25 } })   // Less than
db.users.find({ age: { $lte: 25 } })  // Less than or equal
db.users.find({ age: { $ne: 25 } })   // Not equal

// Logical operators
db.users.find({
  $or: [
    { city: "Mumbai" },
    { city: "Delhi" }
  ]
})

db.users.find({
  $and: [
    { age: { $gt: 20 } },
    { age: { $lt: 30 } }
  ]
})

// Array operators
db.users.find({ hobbies: { $in: ["coding", "reading"] } })
db.users.find({ tags: { $all: ["electronics", "laptop"] } })

// Include only name and email (exclude _id)
db.users.find(
  { city: "Mumbai" },
  { name: 1, email: 1, _id: 0 }
)

// Exclude password
db.users.find(
  { email: "vivek@example.com" },
  { password: 0 }
)

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

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

// Limit results
db.users.find().limit(5)

// Skip results (pagination)
db.users.find().skip(10).limit(5)

// Chain operations
db.users.find({ city: "Mumbai" })
  .sort({ age: -1 })
  .skip(0)
  .limit(10)

// Update one document
db.users.updateOne(
  { name: "Vivek Sharma" },        // Filter
  { $set: { age: 26, city: "Pune" } }  // Update
)

// Output:
{ acknowledged: true, matchedCount: 1, modifiedCount: 1 }

// Update all users in Mumbai
db.users.updateMany(
  { city: "Mumbai" },
  { $set: { state: "Maharashtra" } }
)

// Increment age by 1 for all users
db.users.updateMany(
  {},
  { $inc: { age: 1 } }
)

// Add element to array
db.users.updateOne(
  { name: "Vivek" },
  { $push: { hobbies: "swimming" } }
)

// Add multiple elements
db.users.updateOne(
  { name: "Vivek" },
  { $push: { hobbies: { $each: ["cycling", "traveling"] } } }
)

// Remove element from array
db.users.updateOne(
  { name: "Vivek" },
  { $pull: { hobbies: "gaming" } }
)

// Add to array if not exists
db.users.updateOne(
  { name: "Vivek" },
  { $addToSet: { hobbies: "reading" } }
)

// Update and return updated document
db.users.findOneAndUpdate(
  { name: "Vivek Sharma" },
  { $set: { age: 27 } },
  { returnNewDocument: true }
)

// Update and return original document
db.users.findOneAndUpdate(
  { name: "Vivek Sharma" },
  { $set: { age: 27 } }
)

// Replace entire document (except _id)
db.users.replaceOne(
  { name: "Vivek Sharma" },
  {
    name: "Vivek Kumar",
    email: "vivek@example.com",
    age: 28,
    city: "Chennai"
  }
)

// Delete first matching document
db.users.deleteOne({ name: "Amit Kumar" })

// Output:
{ acknowledged: true, deletedCount: 1 }

// Delete by _id
db.users.deleteOne({ _id: ObjectId("65f1a2b3c4d5e6f7g8h9i0j1") })

// Delete all users from Delhi
db.users.deleteMany({ city: "Delhi" })

// Delete users older than 30
db.users.deleteMany({ age: { $gt: 30 } })

// Delete all documents (be careful!)
db.users.deleteMany({})

// Delete and return deleted document
const deletedUser = db.users.findOneAndDelete(
  { name: "Vivek Sharma" }
)

// Output: Returns the deleted document

// Comparison Operators
$eq  - Equal to          { age: { $eq: 25 } }
$ne  - Not equal to      { age: { $ne: 25 } }
$gt  - Greater than      { age: { $gt: 25 } }
$gte - Greater or equal  { age: { $gte: 25 } }
$lt  - Less than         { age: { $lt: 25 } }
$lte - Less or equal     { age: { $lte: 25 } }
$in  - In array          { city: { $in: ["Mumbai", "Delhi"] } }
$nin - Not in array      { city: { $nin: ["Mumbai"] } }

// Logical Operators
$or  - OR condition      { $or: [ { age: 25 }, { city: "Mumbai" } ] }
$and - AND condition     { $and: [ { age: 25 }, { city: "Mumbai" } ] }
$not - NOT condition     { age: { $not: { $gt: 25 } } }
$nor - NOR condition     { $nor: [ { age: 25 }, { city: "Mumbai" } ] }

// Element Operators
$exists - Field exists   { email: { $exists: true } }
$type   - Field type     { age: { $type: "number" } }

// Array Operators
$all   - All elements    { tags: { $all: ["mongodb", "express"] } }
$size  - Array size      { hobbies: { $size: 3 } }

// Find users between age 20 and 30
db.users.find({ age: { $gt: 20, $lt: 30 } })

// Find users from Mumbai or Delhi
db.users.find({ city: { $in: ["Mumbai", "Delhi"] } })

// Find users with age > 25 OR city Mumbai
db.users.find({
  $or: [
    { age: { $gt: 25 } },
    { city: "Mumbai" }
  ]
})

// Find users with email field exists
db.users.find({ email: { $exists: true } })

// Find users with at least 3 hobbies
db.users.find({ hobbies: { $size: 3 } })