Please refer to the article Polling System Basic Low-Level Design - I
Let's break down the entire process into detailed steps, including the database setup, API implementation using Node.js with Express, and interaction with MySQL. We will cover:
First, we'll define the schema for the MySQL database and create the necessary tables.
CREATE DATABASE polling_system; USE polling_system; CREATE TABLE polls ( poll_id INT AUTO_INCREMENT PRIMARY KEY, question VARCHAR(255) NOT NULL, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ); CREATE TABLE options ( option_id INT AUTO_INCREMENT PRIMARY KEY, poll_id INT, option_text VARCHAR(255) NOT NULL, FOREIGN KEY (poll_id) REFERENCES polls(poll_id) ON DELETE CASCADE ); CREATE TABLE votes ( vote_id INT AUTO_INCREMENT PRIMARY KEY, poll_id INT, user_id VARCHAR(255) NOT NULL, option_id INT, created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP, FOREIGN KEY (poll_id) REFERENCES polls(poll_id) ON DELETE CASCADE, FOREIGN KEY (option_id) REFERENCES options(option_id) ON DELETE CASCADE );
polls table: Stores poll information with a unique identifier, question, and creation timestamp.
options table: Stores the options associated with a poll, linked via poll_id.
votes table: Records each vote, linking to the poll, option, and user.
Entities:
Relationships:
Here’s a description of the ERD:
Polls Table:
Options Table:
Votes Table:
The relationships would be represented with lines between the entities:
Let's set up a Node.js project using Express and MySQL.
mkdir polling-system cd polling-system npm init -y npm install express mysql2 dotenv
Create a basic structure for the project:
polling-system/ │ ├── .env ├── index.js ├── db/ │ └── db.js ├── routes/ │ └── pollRoutes.js └── controllers/ └── pollController.js
File - db/db.js
const mysql = require('mysql2/promise'); require('dotenv').config(); const pool = mysql.createPool({ host: process.env.DB_HOST, user: process.env.DB_USER, password: process.env.DB_PASSWORD, database: process.env.DB_NAME, waitForConnections: true, connectionLimit: 10, queueLimit: 0 }); module.exports = pool;
File - .env
DB_HOST=localhost DB_USER=root DB_PASSWORD=yourpassword DB_NAME=polling_system PORT=3000
File - controllers/pollController.js
This file will implement all the necessary CRUD operations for the polling system.
const pool = require('../db/db'); // Create Poll exports.createPoll = async (req, res) => { const { question, options } = req.body; if (!question || !options || !Array.isArray(options) || options.length { return connection.execute( 'INSERT INTO options (poll_id, option_text) VALUES (?, ?)', [pollId, option] ); }); await Promise.all(optionQueries); await connection.commit(); connection.release(); res.status(201).json({ pollId, message: "Poll created successfully." }); } catch (error) { console.error("Error creating poll:", error.message); res.status(500).json({ message: "Error creating poll." }); } }; // Update Poll exports.updatePoll = async (req, res) => { const { pollId } = req.params; const { question, options } = req.body; if (!pollId || !question || !options || !Array.isArray(options) || options.length { return connection.execute( 'INSERT INTO options (poll_id, option_text) VALUES (?, ?)', [pollId, option] ); }); await Promise.all(optionQueries); await connection.commit(); connection.release(); res.status(200).json({ message: "Poll updated successfully." }); } catch (error) { console.error("Error updating poll:", error.message); res.status(500).json({ message: "Error updating poll." }); } }; // Delete Poll exports.deletePoll = async (req, res) => { const { pollId } = req.params; try { const connection = await pool.getConnection(); const [result] = await connection.execute( 'DELETE FROM polls WHERE poll_id = ?', [pollId] ); connection.release(); if (result.affectedRows === 0) { return res.status(404).json({ message: "Poll not found." }); } res.status(200).json({ message: "Poll deleted successfully." }); } catch (error) { console.error("Error deleting poll:", error.message); res.status(500).json({ message: "Error deleting poll." }); } }; // Vote in Poll exports.voteInPoll = async (req, res) => { const { pollId } = req.params; const { userId, option } = req.body; if (!userId || !option) { return res.status(400).json({ message: "User ID and option are required." }); } try { const connection = await pool.getConnection(); const [userVote] = await connection.execute( 'SELECT * FROM votes WHERE poll_id = ? AND user_id = ?', [pollId, userId] ); if (userVote.length > 0) { connection.release(); return res.status(400).json({ message: "User has already voted." }); } const [optionResult] = await connection.execute( 'SELECT option_id FROM options WHERE poll_id = ? AND option_text = ?', [pollId, option] ); if (optionResult.length === 0) { connection.release(); return res.status(404).json({ message: "Option not found." }); } const optionId = optionResult[0].option_id; await connection.execute( 'INSERT INTO votes (poll_id, user_id, option_id) VALUES (?, ?, ?)', [pollId, userId, optionId] ); connection.release(); res.status(200).json({ message: "Vote cast successfully." }); } catch (error) { console.error("Error casting vote:", error.message); res.status(500).json({ message: "Error casting vote." }); } }; // View Poll Results exports.viewPollResults = async (req, res) => { const { pollId } = req.params; try { const connection = await pool.getConnection(); const [poll] = await connection.execute( 'SELECT * FROM polls WHERE poll_id = ?', [pollId] ); if (poll.length === 0) { connection.release(); return res.status(404).json({ message: "Poll not found." }); } const [options] = await connection.execute( 'SELECT option_text, COUNT(votes.option_id) as vote_count FROM options ' 'LEFT JOIN votes ON options.option_id = votes.option_id ' 'WHERE options.poll_id = ? GROUP BY options.option_id', [pollId] ); connection.release(); res.status(200).json({ pollId: poll[0].poll_id, question: poll[0].question, results: options.reduce((acc, option) => { acc[option.option_text] = option.vote_count; return acc; }, {}) }); } catch (error) { console.error("Error viewing poll results:", error.message); res.status(500).json({ message: "Error viewing poll results." }); } };
File - routes/pollRoutes.js
Define the routes for each API endpoint:
const express = require('express'); const router = express.Router(); const pollController = require('../controllers/pollController'); // Routes router.post('/polls', pollController.createPoll); router.put('/polls/:pollId', pollController.updatePoll); router.delete('/polls/:pollId', pollController.deletePoll); router.post('/polls/:pollId/vote', pollController.voteInPoll); router.get('/polls/:pollId/results', pollController.viewPollResults); module.exports = router;
File - index.js
Finally, set up the server:
const express = require('express'); const pollRoutes = require('./routes/pollRoutes'); require('dotenv').config(); const app = express(); app.use(express.json()); // Routes app.use('/api', pollRoutes); // Error Handling Middleware app.use((err, req, res, next) => { console.error(err.stack); res.status(500).json({ message: "Internal server error" }); }); // Start Server const PORT = process.env.PORT || 3000; app.listen(PORT, () => { console.log(`Server is running on port ${PORT}`); });
Each method includes error handling for common issues like invalid input, duplicate votes, missing poll or option, and server errors.
Test each endpoint using tools like Postman or curl.
This is a comprehensive modular implementation of an online polling system using Node.js, Express, and MySQL. It handles the basic CRUD operations and ensures data consistency with transactions. It also includes basic error handling to make the API more robust and user-friendly.
Please refer to the article Polling System Basic Low-Level Design - I
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