Inventory Management System API

A robust backend-heavy API built with Node.js, Express, and MongoDB to track and manage products in a warehouse. This project features full CRUD functionality for products and intelligent inventory logic to handle stock updates safely and efficiently.

Core Features

Product Management: Full CRUD (Create, Read, Update, Delete) endpoints for products.

• Atomic Stock Operations: Safely increase or decrease product stock with logic that prevents race conditions and ensures data integrity.
• Inventory Validation: Business logic to prevent stock quantities from ever going below zero.
• Low Stock Alerts: An endpoint to quickly identify all products that have fallen below their specified low-stock threshold.
• Unit & Integration Testing: A complete test suite using Jest and an in-memory database to validate the API's business logic.

Tech Stack

• Backend: Node.js, Express.js
• Database: MongoDB with Mongoose ODM
• Testing: Jest, Supertest, MongoDB-in-memory-server

Getting Started

Follow these instructions to get the project set up and running on your local machine.

Prerequisites

Make sure you have the following installed:

• Node.js (v14 or newer)
• npm
• MongoDB (for local development database)

Installation & Setup

Clone the repository:

git clone <your-repository-link>
cd <repository-name>

Install dependencies:

npm install

Set up environment variables: Create a file named .env in the root of the project and add the following variables. Replace the placeholder with your own MongoDB connection string.

MONGO_URI="mongodb://localhost:27017/inventoryDB"
PORT=5000

Running the Application

To start the server, run the following command:

npm start

The API will be available at http://localhost:5000.

Running the Test Cases

To run the automated tests, use the following command. The tests use an in-memory MongoDB instance and do not require a separate database connection.

npm test

API Endpoints

All endpoints are prefixed with /api

Method	Endpoint	Description
POST	/products	Creates a new product.
GET	/products	Retrieves a list of all products.
GET	/products/stock/low	Retrieves products below their stock threshold.
GET	/products/:id	Retrieves a single product by its ID.
PATCH	/products/:id	Updates a product's details.
DELETE	/products/:id	Deletes a product by its ID.
PATCH	/products/:id/increase-stock	Increases the stock of a specific product.
PATCH	/products/:id/decrease-stock	Decreases the stock of a specific product.

Assumptions & Design Choices

• RESTful API Design: The API is structured following REST principles, with endpoints grouped by the "product" resource. Actions like increasing stock are handled as sub-resources (/products/:id/increase-stock) for clarity.
• Atomic Operations: To prevent race conditions during concurrent stock updates, the system uses atomic MongoDB operations ($inc, findOneAndUpdate with query conditions) instead of a "read-then-write" pattern. This ensures that the database is the single source of truth and maintains data integrity.
• Data Validation: Business rules, such as preventing negative stock, are enforced at the database schema level using Mongoose validators. This provides a robust and centralized layer of data validation.
• Isolated Testing Environment: Tests are designed to be self-contained and reliable by using an in-memory MongoDB server. This ensures that running tests does not affect any development data and provides a fresh, predictable state for each test run.