🖥️ Backend Mastery: From Zero to Backend Hero 🔥

NOTE:- The "must_change.env" must require some changes;
     > remove the word "must_change.env" and change it into ".env" only
     > replace values with your own credentials inside .env file

📅 Day 01

"The journey of a thousand miles begins with one step."

1. Project Initialization

   • package.json setup
   • Install Express & dotenv
     

2. Configuration

   • Create .env file (PORT)
   • Build server (index.js)
     

3. Routing & Server

   • Define GET routes (/, /login, /signup)
   • Start server

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📅 Day 02

"Code is like humor. When you have to explain it, it’s bad."

1. API Fundamentals

   • What is an API
   • Role in frontend-backend communication
     

2. Working with APIs in React

   • Fetch vs Axios comparison
   • Axios GET request with then() & catch()
   • Best practices (useEffect, useState, error handling)
     

3. Handling CORS Issues

   • What is CORS
   • Proxy setup in Vite
   • Backend solutions (cors package, headers)

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📅 Day 03

"Structure your data before you build — clean models lead to clean code."

1. Data Modeling Basics

   • Object modeling purpose
   • Benefits of early planning
     

2. Introduction to Mongoose

   • What is Mongoose
   • Schemas and models
     

3. Project Structure & Naming Conventions

   • models/ folder setup
   • File naming patterns
     

4. Schema Definition Essentials

   • Field types and rules
   • Common validations (required, unique, min, etc.)
   • Timestamps for created/updated tracking
   • Model Relationships: Using ref for associations

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📅 Day 04

"Learning to write programs stretches your mind, and helps you think better."

1. Data Modeling Practice

   • E-Commerce Store Schema Design
   • Hospital Management System Schema Design
     

2. Exploring Mongoose Concepts

   • Review: models/ecommerce/
   • Review: models/hospital_management/

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📅 Day 05

"A well-structured project is the foundation of professional software development."

1. UI/UX Design & DB Planning Phase

   • Design all screens using tools like Figma
   • Collect data points for DB
   • Create data modeling diagram (with tools like Eraser.io)
     

2. Project Initialization & Structuring

   • Initialize package.json with npm init
   • Setup common folders: src, public, controllers, routes, etc.
   • Create essential files: .env, .gitignore, README.md, etc.
     

3. Development Tools Setup

   • Install nodemon for auto-restart
   • Install prettier for consistent formatting
     

4. Files Configuration

   • Use online generator to create .gitignore for Node.js
   • Add .prettierrc and .prettierignore files
   • Update package.json for modules and scripts

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📅 Day 06

"Build software the way real teams do – step by step, piece by piece."

1. MongoDB Atlas

   • Create account, project, cluster
   • Save URI in .env
     

2. DB Connection

   • Two connection approaches: Direct connect in index.js (less modular) Use src/db/connection.js
   • Best Practices: Use async/await + try/catch
     

3. Import Rules

   • Load dotenv at top of entry file
   • Add .js extension to imports
   • Keep secrets in .env
   • Keep index.js clean

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📅 Day 07

"Building real-world back-end architecture step by step."

1. Express App Setup (app.js)

   • Middlewares: cors, cookieParser, express.json, etc.
     

2. Server Initialization (index.js)

   • DB connection, server start, and error handling
     

3. Utility Modules (utils/)

   • asyncHandler.js – async error wrapper
   • ApiError.js – custom error class
   • ApiResponse.js – consistent success responses

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📅 Day 08

"Professional backend development through real-world modeling techniques."

1. Model Structure & Setup

   • Created user.model.js and video.model.js using Mongoose
   • Used ObjectId references, timestamps, and schema validation
     
     

2. User Model & Authentication

   • Defined user fields
   • Password hashing with bcrypt using Mongoose pre-save middleware
   • Custom methods for authentication:
     • Password verification (bcrypt)
     • JWT generation (jsonwebtoken) for access & refresh tokens
   • Stored secrets and token expiry settings in .env
     

3. Video Model & Pagination

   • Defined video fields
   • Linked each video to its owner (User)
   • Added pagination support using mongoose-aggregate-paginate-v2

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📅 Day 09

"Code is the bridge between imagination and reality; every bug you fix is a step forward."

1. Cloudinary Setup

   • Creating an account and adding credentials in .env
   • Installing npm package cloudinary and configure
   • Functions to upload files and handle errors
     

2. Multer Setup

   • Installing npm package multer
   • Define multer as middleware
   • Multer uses for temporary file storage, and works with Cloudinary

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📅 Day 10

"The web speaks in protocols — learn their language to unlock endless possibilities."

1. HTTP Basics

   • Overview
   • HTTP vs HTTPS
   • Client-Server Model
   • URL, URI, URN
     

2. HTTP Headers

   • Purpose and importance
   • Types: Request, Response, Representation, Payload
   • Key headers: Authorization, Content-Type, CORS
     

3. HTTP Methods

   • Main verbs: GET, POST, PUT, PATCH, DELETE
   • Others: HEAD, OPTIONS, TRACE
     

4. HTTP Status Codes

   • Categories: 1xx to 5xx
   • Common codes: 200, 201, 400, 401, 403, 404, 500

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📅 Day 11

"Building like a pro — following real-world back-end development practices."

1. Express Router & Route Management

   • Using Express Router
   • Exporting and importing router in app.js
   • Mounting routes with app.use()
     

2. Controller Functions & JSON Responses

   • Writing controller functions
   • Sending JSON responses with status codes
   • Example: registerUser controller returning a success message
     

3. Error Handling with asyncHandler

   • Wrapping controllers to handle async errors
   • Avoiding repetitive try-catch blocks
   • Passing errors to Express using next(error)
     

4. API Testing with Postman

   • Creating collections and requests
   • Testing POST routes like /register
   • Verifying JSON response and status codes

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📅 Day 12

"Building like real professionals, one step at a time."

1. User Registration Workflow

   • Input validation and duplication checks
   • Image handling and upload (avatar, cover)
   • User creation and sensitive data filtering
   • Structured API response to frontend
     

2. File Management

   • Local file handling with Multer
   • Cloudinary integration for media uploads
     

3. Error Handling & API Response

   • Centralized error responses using ApiError
   • Consistent success responses via ApiResponse

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📅 Day 13

"Building like real devs — one step at a time."

1. User Registration API

   • Testing /api/v1/users/register using POSTMAN
   • Required form-data fields: fullName, email, username, password, avatar, coverImage
   • Backend tasks: validation, duplication checks, Cloudinary upload, DB save, response handling
     

2. Cloudinary Bug Fixes

   • Bug in cloudinary.js due to delayed dotenv.config()
   • Environment variables not loading (CLOUDINARY_CLOUD_NAME, etc.)
   • Fixes applied in:
     • src/index.js (moved dotenv.config() above imports)
     • package.json (nodemon -r dotenv/config ...)
       

3. Local File Cleanup After Upload

   • Deleting uploaded files from public/temp after Cloudinary upload
   • Using fs.unlinkSync() in both success and error cases
     

4. Professional Use of POSTMAN

   • Organizing with Collections (e.g., MediaTube) and Folders (e.g., user)
   • Creating and using Environment Variables (server = base URL)
   • Replacing hardcoded URLs with {{server}} variable in requests

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📅 Day 14

"Building a real-world back-end system using professional development practices."

1. Authentication Flow

   • /login Route
   • /logout Route
   • loginUser Controller
   • logoutUser Controller
     

2. Token Management

   • Access & Refresh Token Generator
   • Sending Tokens as Secure Cookies
   • Removing Tokens via Cookies on Logout
     

3. Security Middleware

   • verifyJWT Middleware for Protected Routes
   • Token Validation via Cookies or Headers

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📅 Day 15

"Simulating a real-world back-end development process used in professional software companies."

1. Authentication Route Testing

   • Testing /login and /logout using POSTMAN
   • Expected request structure and responses
   • Cookie handling for tokens
     

2. Login Controller Debugging

   • Common login issues (missing fields, invalid credentials, etc.)
   • Proper use of async/await and error handling
   • Security tips: avoid exposing sensitive data
     

3. Token-Based Authentication

   • Access Token: purpose, lifespan, and usage
   • Refresh Token: role in session management and renewal
   • Key differences between access and refresh tokens
   • How both tokens work together in maintaining user sessions
     

4. Refresh Token Implementation

   • /refresh-token route functionality
   • Validating refresh tokens and issuing new tokens
   • Security practices: HttpOnly cookies, database checks
   • Frontend behavior on token expiration

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📅 Day 16

"Building a scalable backend by following real-world development practices."

1. Subscription Model

   • Mongoose schema for user-to-user subscriptions
   • Fields: subscriber, channel (both linked to User model)
   • Includes timestamps for creation and updates
     

2. User Account Management

   • Password Management: Change current password with verification

   • Profile Information: Get current logged-in user details Update full name and email (excluding password)

   • Media Uploads: Update user avatar (profile picture) Update cover image (banner)

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📅 Day 17

"Note:- You can see the 'day 17.png' image for visual understanding"

1. Designing the Subscription Model

   • Purpose of the Subscription Model
   • Why not use arrays in the User schema
   • One subscription per document structure
   • Advantages of this Approach
     

2. Querying Subscriptions

   • Counting a channel’s subscribers
   • Listing channels a user has subscribed to

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📅 Day 18

"Building real-world features using professional backend practices."

1. MongoDB Aggregation Pipeline

   • What is Aggregation Pipeline
   • Why and when to use it
   • Benefits for complex data querying
     

2. Aggregation Stages

   • $match – Filter documents
   • $lookup – Join collections
   • $addFields – Add or modify fields
   • $project – Select specific fields
   • $sort, $limit, $group, $unwind
     

3. Common Operators

   • $in – Check if value exists in array
   • $cond – If-then-else logic
   • $size, $eq, $and, $or

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📅 Day 19

"Building real-world back-end features, step by step, like a pro."

1. Watch History Feature

   • Defining getWatchHistory controller
   • MongoDB Aggregation Pipeline usage
   • Step-by-step data retrieval and joining
     

2. User Routes & Structure

   • Defining routes for controllers
   • Public Routes: /register, /login
   • Protected Routes: /logout, /history, /update-account, etc.
     

3. Route Protection & Middleware

   • JWT authentication using verifyJWT
   • File upload handling with upload middleware

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📅 Day 20

"Expanding the backend with essential user and content models."

1. Created More Models

   • Comment Model - content, video, owner

   • Like Model - video | comment | tweet, likedBy

   • Playlist Model - name, description, videos, owner

   • Tweet Model - content, owner

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📅 Day 21

Simple structure, clear steps, professional workflow.

1. User Routes Tested

   • Tested all user routes using Postman
   • Fixed small bugs
   • Now user routes are working perfectly
     

2. Routes & Controllers Setup

   • All routes defined in app.js
   • Created routes in src/routes/ for:
     • tweet, video, comment, like, playlist, subscription, dashboard
   • Created controllers in src/controllers/ with:
     • Empty methods
     • // TASK: comments showing what logic to add later
       

3. What Do Next

   • Add real logic inside controller methods
   • Test each route using Postman
   • Make sure everything works correctly