WebDevRoadmap21_30.ipynb

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        "Here’s the detailed guide for **Days 21-30: Back-End Development** with in-depth explanations, examples, and practice problems.\n",
        "\n",
        "---\n",
        "\n",
        "# **Web Development Roadmap: Days 21-30 - Back-End Development**\n",
        "\n",
        "## **Overview**\n",
        "\n",
        "In this phase, you'll focus on server-side development, including setting up servers, working with databases, and managing user authentication. You’ll build the skills needed to handle data, create APIs, and connect your front-end to a back-end system.\n",
        "\n",
        "---\n",
        "\n",
        "## **Day 21-23: Node.js & Express.js**\n",
        "\n",
        "### **1.1 Node.js Basics**\n",
        "\n",
        "**Introduction**:\n",
        "- **Node.js**: A JavaScript runtime built on Chrome's V8 engine, allowing you to run JavaScript on the server side.\n",
        "\n",
        "**Setting Up Node.js**:\n",
        "- **Installation**: Download and install Node.js from [nodejs.org](https://nodejs.org/).\n",
        "- **Creating a Basic Server**:\n",
        "\n",
        "```javascript\n",
        "// index.js\n",
        "const http = require('http');\n",
        "\n",
        "const hostname = '127.0.0.1';\n",
        "const port = 3000;\n",
        "\n",
        "const server = http.createServer((req, res) => {\n",
        "  res.statusCode = 200;\n",
        "  res.setHeader('Content-Type', 'text/plain');\n",
        "  res.end('Hello World\\n');\n",
        "});\n",
        "\n",
        "server.listen(port, hostname, () => {\n",
        "  console.log(`Server running at http://${hostname}:${port}/`);\n",
        "});\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Create a Node.js server that responds with different messages based on the URL path (`/home`, `/about`, etc.).\n",
        "2. Set up a basic server that reads and serves an HTML file.\n",
        "\n",
        "### **1.2 Express.js**\n",
        "\n",
        "**Introduction**:\n",
        "- **Express.js**: A web framework for Node.js that simplifies routing and handling HTTP requests.\n",
        "\n",
        "**Setting Up Express**:\n",
        "- **Installation**: Use npm to install Express.\n",
        "\n",
        "```bash\n",
        "npm install express\n",
        "```\n",
        "\n",
        "- **Basic Express Server**:\n",
        "\n",
        "```javascript\n",
        "// app.js\n",
        "const express = require('express');\n",
        "const app = express();\n",
        "const port = 3000;\n",
        "\n",
        "app.get('/', (req, res) => {\n",
        "  res.send('Hello World');\n",
        "});\n",
        "\n",
        "app.listen(port, () => {\n",
        "  console.log(`Server running at http://localhost:${port}/`);\n",
        "});\n",
        "```\n",
        "\n",
        "**Routing**:\n",
        "- **Basic Routing**:\n",
        "\n",
        "```javascript\n",
        "app.get('/about', (req, res) => {\n",
        "  res.send('About Page');\n",
        "});\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Create an Express server with multiple routes, such as `/`, `/services`, and `/contact`.\n",
        "2. Set up a server that serves static files from a `public` directory.\n",
        "\n",
        "---\n",
        "\n",
        "## **Day 24-26: Databases**\n",
        "\n",
        "### **2.1 SQL Databases**\n",
        "\n",
        "**Introduction**:\n",
        "- **SQL**: Structured Query Language used for managing relational databases.\n",
        "\n",
        "**Basic SQL Commands**:\n",
        "- **Creating Tables**:\n",
        "\n",
        "```sql\n",
        "CREATE TABLE users (\n",
        "    id INT AUTO_INCREMENT PRIMARY KEY,\n",
        "    name VARCHAR(255) NOT NULL,\n",
        "    email VARCHAR(255) NOT NULL UNIQUE,\n",
        "    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP\n",
        ");\n",
        "```\n",
        "\n",
        "- **Inserting Data**:\n",
        "\n",
        "```sql\n",
        "INSERT INTO users (name, email) VALUES ('John Doe', 'john@example.com');\n",
        "```\n",
        "\n",
        "- **Querying Data**:\n",
        "\n",
        "```sql\n",
        "SELECT * FROM users;\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Design a database schema for a blog with tables for users, posts, and comments.\n",
        "2. Write SQL queries to retrieve all posts by a specific user and count the number of comments on each post.\n",
        "\n",
        "### **2.2 NoSQL Databases**\n",
        "\n",
        "**Introduction**:\n",
        "- **MongoDB**: A NoSQL database that stores data in JSON-like documents.\n",
        "\n",
        "**Basic MongoDB Commands**:\n",
        "- **Creating a Collection**:\n",
        "\n",
        "```javascript\n",
        "// Using MongoDB Shell\n",
        "db.createCollection(\"users\");\n",
        "```\n",
        "\n",
        "- **Inserting Documents**:\n",
        "\n",
        "```javascript\n",
        "db.users.insertOne({ name: \"Jane Doe\", email: \"jane@example.com\" });\n",
        "```\n",
        "\n",
        "- **Querying Documents**:\n",
        "\n",
        "```javascript\n",
        "db.users.find();\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Create a MongoDB collection for a to-do list application and insert sample tasks.\n",
        "2. Write a query to find all tasks that are marked as incomplete and sort them by due date.\n",
        "\n",
        "---\n",
        "\n",
        "## **Day 27-30: Authentication & Authorization**\n",
        "\n",
        "### **3.1 User Authentication**\n",
        "\n",
        "**Introduction**:\n",
        "- **Authentication**: Verifying the identity of a user.\n",
        "\n",
        "**Using Passport.js**:\n",
        "- **Installation**: Install Passport.js and related packages.\n",
        "\n",
        "```bash\n",
        "npm install passport passport-local express-session\n",
        "```\n",
        "\n",
        "- **Basic Setup**:\n",
        "\n",
        "```javascript\n",
        "const passport = require('passport');\n",
        "const LocalStrategy = require('passport-local').Strategy;\n",
        "const expressSession = require('express-session');\n",
        "\n",
        "app.use(expressSession({ secret: 'secret', resave: false, saveUninitialized: false }));\n",
        "app.use(passport.initialize());\n",
        "app.use(passport.session());\n",
        "\n",
        "passport.use(new LocalStrategy(\n",
        "  function(username, password, done) {\n",
        "    // Authentication logic here\n",
        "  }\n",
        "));\n",
        "\n",
        "passport.serializeUser(function(user, done) {\n",
        "  done(null, user.id);\n",
        "});\n",
        "\n",
        "passport.deserializeUser(function(id, done) {\n",
        "  // Fetch user by ID\n",
        "});\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Implement a user login system using Passport.js and a local strategy.\n",
        "2. Add a registration route where users can create an account.\n",
        "\n",
        "### **3.2 Authorization**\n",
        "\n",
        "**Introduction**:\n",
        "- **Authorization**: Controlling access to resources based on user roles.\n",
        "\n",
        "**Implementing Authorization**:\n",
        "- **Role-Based Access Control**:\n",
        "\n",
        "```javascript\n",
        "function ensureAuthenticated(req, res, next) {\n",
        "  if (req.isAuthenticated()) {\n",
        "    return next();\n",
        "  }\n",
        "  res.redirect('/login');\n",
        "}\n",
        "\n",
        "app.get('/admin', ensureAuthenticated, (req, res) => {\n",
        "  res.send('Admin Page');\n",
        "});\n",
        "```\n",
        "\n",
        "**Practice Problems**:\n",
        "1. Add role-based access to a route so that only users with an `admin` role can access it.\n",
        "2. Create middleware that restricts access based on user permissions.\n",
        "\n",
        "---\n",
        "\n",
        "This guide provides a detailed look into server-side development and database management. By completing the practice problems and implementing the examples, you’ll gain a solid understanding of how to build and manage the back-end of web applications. Feel free to reach out if you need further details or have any questions!\n",
        "\n"
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