MongoDB Playground Examples - Beginner Friendly Guide

This repository contains MongoDB Playground scripts tested in VS Code.
It helps you learn MongoDB step by step with examples and explanations.

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Table of Contents

1. What is MongoDB?
2. Key Components
3. Installing MongoDB
4. Basic Mongo Shell Commands
5. CRUD Operations
6. Aggregation Framework
7. Indexing
8. How to Run

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What is MongoDB?

• MongoDB is a NoSQL database.
• It stores data in JSON-like documents (actually BSON).
• Unlike SQL databases, MongoDB does not use tables and rows, but collections and documents.

Example Document:

{
  "name": "Alice",
  "age": 25,
  "city": "Delhi"
}

Explanation:

• Each document is like a record.
• A collection is like a table.

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Key Components

Component	Description
mongod	Mongo Daemon is mongoDB server engine. Stores data, handles queries, indexes, and connections. Usually runs automatically in background as a service in modern setups.
mongosh	MongoDB shell. Command-line interface to run queries.
MongoDB Compass	GUI tool to visualize data, run queries, and analyze performance. Connects to mongod automatically.

💡 Tip: Beginners can start with MongoDB Compass to see documents visually.

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Installing MongoDB

1. Go to MongoDB Community Download.
2. Download Community Edition for your OS.
3. Install following instructions.
4. Start the server using:

mongod

5. Open a new terminal for the shell:

mongosh

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Basic Mongo Shell Commands

Command	Explanation	Example
show dbs	Lists all databases	show dbs
use <dbName>	Switch or create a database	use ecommerce
show collections	Lists collections in current DB	show collections
db.dropDatabase()	Deletes current database	db.dropDatabase()

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CRUD Operations

CRUD = Create, Read, Update, Delete

1. Create (Insert)

// Insert one document
db.users.insertOne({
  name: "Alice",
  age: 25,
  city: "Delhi",
});

// Insert many documents
db.users.insertMany([
  { name: "Bob", age: 28, city: "Mumbai" },
  { name: "Charlie", age: 30, city: "Bangalore" },
]);

Explanation:

• insertOne adds one document.
• insertMany adds multiple documents at once.

Expected Output:

{
  "acknowledged": true,
  "insertedId": ObjectId("...")
}

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2. Read (Query)

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

// Find users in Delhi
db.users.find({ city: "Delhi" });

// Find specific fields
db.users.find({}, { name: 1, city: 1 });

// Comparison operators
db.users.find({ age: { $gt: 25 } }); // age > 25
db.users.find({ age: { $lte: 30 } }); // age <= 30

Explanation:

• { city: "Delhi" } is a filter.
• { name: 1, city: 1 } shows only name and city fields.
• $gt = greater than, $lte = less than or equal.

Expected Output:

[
  { "name": "Bob", "city": "Mumbai" },
  { "name": "Charlie", "city": "Bangalore" }
]

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3. Update

// Update one document
db.users.updateOne({ name: "Alice" }, { $set: { city: "Noida" } });

// Update multiple documents
db.users.updateMany({ city: "Mumbai" }, { $set: { verified: true } });

Explanation:

• $set changes or adds fields.
• updateOne updates the first matching document.
• updateMany updates all matching documents.

Expected Output:

{
  "acknowledged": true,
  "modifiedCount": 1
}

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4. Delete

// Delete one
db.users.deleteOne({ name: "Charlie" });

// Delete many
db.users.deleteMany({ verified: false });

Explanation:

• Deletes documents matching the filter.

Expected Output:

{ "acknowledged": true, "deletedCount": 1 }

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Aggregation Framework

Used for advanced data analysis (like SQL GROUP BY).

db.orders.aggregate([
  { $match: { status: "delivered" } },
  {
    $group: {
      _id: "$customerId",
      totalAmount: { $sum: "$amount" },
      orderCount: { $sum: 1 },
    },
  },
  { $sort: { totalAmount: -1 } },
]);

Explanation:

1. $match filters documents.
2. $group groups by customerId and calculates totals.
3. $sort sorts by totalAmount descending.

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Indexing

// Single-field index
db.users.createIndex({ name: 1 });

// Compound index
db.users.createIndex({ city: 1, age: -1 });

// List indexes
db.users.getIndexes();

// Drop an index
db.users.dropIndex("name_1");

Tip: Use indexes on fields you search or sort frequently. Avoid indexing highly updated fields.

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How to Run

1. Open .mongodb.js file in VS Code.
2. Click Run Playground.
3. Or use mongosh manually to run commands.
4. Visualize results using MongoDB Compass.

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