How to use Express JS with Mongoose?

Using Express.js with Mongoose is a common setup for building applications with MongoDB. Here's a step-by-step guide to help you get started:

Step 1: Set Up a New Express.js Project

Initialize a New Project:

   mkdir express-mongoose-app
   cd express-mongoose-app
   npm init -y

Install Required Packages:

   npm install express mongoose
   npm install dotenv

Step 2: Configure Environment Variables

Create a .env File: Create a .env file in the root of your project to store environment variables:

   PORT=3000
   MONGODB_URI=mongodb://localhost:27017/mydatabase

Load Environment Variables: Create a config.js file to load environment variables:

   require('dotenv').config();

   module.exports = {
     port: process.env.PORT || 3000,
     mongodbUri: process.env.MONGODB_URI,
   };

Step 3: Set Up Mongoose

Create a Directory Structure:

   mkdir -p src/models src/controllers src/routes src/config

Create Mongoose Connection: Create src/config/mongoose.js to handle the connection to MongoDB:

   const mongoose = require('mongoose');
   const config = require('../../config');

   const connectDB = async () => {
     try {
       await mongoose.connect(config.mongodbUri, {
         useNewUrlParser: true,
         useUnifiedTopology: true,
         useCreateIndex: true,
         useFindAndModify: false,
       });
       console.log('MongoDB connected');
     } catch (error) {
       console.error('MongoDB connection failed:', error.message);
       process.exit(1);
     }
   };

   module.exports = connectDB;

Step 4: Create Mongoose Models

Create a User Model: Create src/models/User.js:

   const mongoose = require('mongoose');

   const userSchema = new mongoose.Schema({
     name: {
       type: String,
       required: true,
     },
     email: {
       type: String,
       required: true,
       unique: true,
     },
     password: {
       type: String,
       required: true,
     },
   });

   const User = mongoose.model('User', userSchema);

   module.exports = User;

Step 5: Create Controllers

Create User Controller: Create src/controllers/userController.js:

   const User = require('../models/User');

   exports.getUsers = async (req, res) => {
     try {
       const users = await User.find();
       res.json(users);
     } catch (error) {
       res.status(500).json({ message: error.message });
     }
   };

   exports.getUser = async (req, res) => {
     try {
       const user = await User.findById(req.params.id);
       if (!user) {
         return res.status(404).json({ message: 'User not found' });
       }
       res.json(user);
     } catch (error) {
       res.status(500).json({ message: error.message });
     }
   };

   exports.createUser = async (req, res) => {
     const { name, email, password } = req.body;

     const userExists = await User.findOne({ email });
     if (userExists) {
       return res.status(400).json({ message: 'User already exists' });
     }

     const user = new User({
       name,
       email,
       password,
     });

     try {
       const newUser = await user.save();
       res.status(201).json(newUser);
     } catch (error) {
       res.status(400).json({ message: error.message });
     }
   };

   exports.updateUser = async (req, res) => {
     try {
       const user = await User.findById(req.params.id);
       if (!user) {
         return res.status(404).json({ message: 'User not found' });
       }

       user.name = req.body.name || user.name;
       user.email = req.body.email || user.email;
       user.password = req.body.password || user.password;

       const updatedUser = await user.save();
       res.json(updatedUser);
     } catch (error) {
       res.status(400).json({ message: error.message });
     }
   };

   exports.deleteUser = async (req, res) => {
     try {
       const user = await User.findById(req.params.id);
       if (!user) {
         return res.status(404).json({ message: 'User not found' });
       }

       await user.remove();
       res.json({ message: 'User deleted' });
     } catch (error) {
       res.status(500).json({ message: error.message });
     }
   };

Step 6: Create Routes

Create User Routes: Create src/routes/userRoutes.js:

   const express = require('express');
   const { getUsers, getUser, createUser, updateUser, deleteUser } = require('../controllers/userController');

   const router = express.Router();

   router.get('/users', getUsers);
   router.get('/users/:id', getUser);
   router.post('/users', createUser);
   router.put('/users/:id', updateUser);
   router.delete('/users/:id', deleteUser);

   module.exports = router;

Step 7: Set Up the Express Server

Create the Server: Create src/index.js:

   const express = require('express');
   const connectDB = require('./config/mongoose');
   const userRoutes = require('./routes/userRoutes');
   const config = require('../config');

   const app = express();

   // Connect to MongoDB
   connectDB();

   // Middleware to parse JSON
   app.use(express.json());

   // Routes
   app.use('/api', userRoutes);

   const PORT = config.port;
   app.listen(PORT, () => {
     console.log(`Server running on http://localhost:${PORT}`);
   });

Step 8: Run the Application

Start the Express Application:

   node src/index.js

Step 9: Test the API

Test Endpoints:
Use a tool like Postman or curl to test the RESTful API endpoints:
- GET /api/users: Retrieve all users.
- GET /api/users/:id: Retrieve a user by ID.
- POST /api/users: Create a new user.
```
 {
   "name": "John Doe",
   "email": "john@example.com",
   "password": "password"
 }
```

PUT /api/users/:id: Update a user by ID.
DELETE /api/users/:id: Delete a user by ID.

This guide provides a foundational approach to integrating Mongoose with an Express.js application. You can further expand and customize it based on your application's requirements.

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