Epoch 4: Build the Order Service (ExpressJS)

Objectives

• Design and build an order schema using Mongoose.
• Implement CRUD operations for order management.
• Structure order data to reference userId and productId.
• Test order workflows with realistic payloads.
• Understand how microservices communicate via IDs (later: through APIs or message queues).

1. Microservice Overview

• Service Name: order-service
• Responsibility: Manage order catalog including create, update, view, and delete operations.
• Technology Stack: Node.js, ExpressJS, MongoDB, Mongoose

2. Structure architechture

order-service/
├── controllers/
│   └── order.controller.js
├── models/
│   └── order.model.js
├── routes/
│   └── order.routes.js
├── .env
├── server.js
├── package.json

2.1. Project Setup

• Step 1: Initialize the Project

  mkdir order-service
  cd order-service
  npm init -y
  

• Step 2: Install Dependencies

  npm install express mongoose dotenv
  

• Step 3: Project Structure: Create the following folders and files:

  mkdir controllers models routes middlewares
  touch server.js .env
  

2.2. Mongoose Order Schema

• models/order.model.js

const mongoose = require('mongoose');

const orderSchema = new mongoose.Schema({
  userId: { type: String, required: true },
  products: [
    {
      productId: String,
      quantity: Number
    }
  ],
  totalPrice: { type: Number, required: true },
  status: {
    type: String,
    enum: ['pending', 'processing', 'shipped', 'delivered', 'cancelled'],
    default: 'pending'
  },
  createdAt: { type: Date, default: Date.now }
});

module.exports = mongoose.model('Order', orderSchema);

2.3. Order Controller

• controllers/order.controller.js ```js const Order = require(‘../models/order.model’);

exports.createOrder = async (req, res) => { try { const order = await Order.create(req.body); res.status(201).json(order); } catch (err) { res.status(400).json({ error: ‘Failed to create order.’ }); } };

exports.getAllOrders = async (req, res) => { const orders = await Order.find(); res.json(orders); };

exports.getOrderById = async (req, res) => { const order = await Order.findById(req.params.id); if (!order) return res.status(404).json({ error: ‘Order not found’ }); res.json(order); };

exports.updateOrder = async (req, res) => { const order = await Order.findByIdAndUpdate(req.params.id, req.body, { new: true }); if (!order) return res.status(404).json({ error: ‘Order not found’ }); res.json(order); };

exports.deleteOrder = async (req, res) => { const order = await Order.findByIdAndDelete(req.params.id); if (!order) return res.status(404).json({ error: ‘Order not found’ }); res.json({ message: ‘Order deleted successfully’ }); };

### 2.4. Routes
- routes/order.routes.js
```js
const express = require('express');
const router = express.Router();
const {
  createOrder,
  getAllOrders,
  getOrderById,
  updateOrder,
  deleteOrder
} = require('../controllers/order.controller');

router.post('/', createOrder);
router.get('/', getAllOrders);
router.get('/:id', getOrderById);
router.put('/:id', updateOrder);
router.delete('/:id', deleteOrder);

module.exports = router;

2.5. Server Setup

• server.js ```js // server.js const express = require(‘express’); const mongoose = require(‘mongoose’); require(‘dotenv’).config();

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

app.use(‘/api/orders’, require(‘./routes/order.routes’));

mongoose.connect(process.env.MONGO_URI) .then(() => app.listen(process.env.PORT, () => { console.log(Order service running on port ${process.env.PORT}); })) .catch(err => console.error(err));

### 2.6. Environment Variables
Create a .env file in the root directory:

PORT=4003 MONGO_URI=mongodb://localhost:27017/order-service ```

3. Testing with Postman

• Example Request Payload { “userId”: “64adfa1…abcd”, “products”: [ { “productId”: “64aef123…xyz”, “quantity”: 2 }, { “productId”: “64aef124…klm”, “quantity”: 1 } ], “totalPrice”: 1999 }

Method	Endpoint	Description	Request Body
POST	/api/orders	Create new order	has Payload
GET	/api/orders	Get all orders	-
GET	/api/orders/:id	Get order by ID	-
PUT	/api/orders/:id	Update order status	has Payload
DELETE	/api/orders/:id	Delete order	-