✅ Add Joi Validation Middleware

Let's add validation using Joi to our existing Node.js + Express blog API, specifically for creating articles.

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📦 Step 1: Install Joi

npm install joi

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📁 Step 2: Create a Middleware File

Create a file: middlewares/validateArticle.js

const Joi = require('joi');

// Define the schema
const articleSchema = Joi.object({
  title: Joi.string().min(3).max(100).required(),
  content: Joi.string().min(10).required(),
  author: Joi.string().min(3).required()
});

// Middleware to validate request body
function validateArticle(req, res, next) {
  const { error } = articleSchema.validate(req.body);
  if (error) {
    return res.status(400).json({ error: error.details[0].message });
  }
  next();
}

module.exports = validateArticle;

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🧠 What this does:

• It checks that:

  • title is a string between 3–100 chars
  • content is at least 10 chars
  • author is required and at least 3 chars

• If validation fails, it sends a 400 response with a message like:
  
  

  "title" is not allowed to be empty

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🧪 Step 3: Use the Middleware in the POST Route

In your route file (or server.js, depending on your structure):

const express = require('express');
const mongoose = require('mongoose');
const cors = require('cors');
const Article = require('./models/article');
const validateArticle = require('./middlewares/validateArticle');

const app = express();
app.use(express.json());
app.use(cors());

// POST with validation middleware
app.post('/api/articles', validateArticle, async (req, res) => {
  try {
    const newArticle = new Article(req.body);
    const savedArticle = await newArticle.save();
    res.status(201).json(savedArticle);
  } catch (err) {
    res.status(500).json({ error: 'Server error while creating article' });
  }
});

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✅ Example of a Valid Request

{
  "title": "How to Use Joi",
  "content": "Joi is a powerful schema description and validation tool...",
  "author": "Xavier"
}

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❌ Example of Invalid Request

{
  "title": "",
  "content": "short",
  "author": ""
}

Response:

{
  "error": "\"title\" is not allowed to be empty"
}

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