🚀 Expense Tracker Backend

A lightweight and scalable FastAPI backend for the Expense Tracker application. This backend provides RESTful APIs to manage expenses, powered by SQLite + SQLAlchemy, and is designed to seamlessly integrate with a Flutter frontend.

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📌 Overview

This backend is built with simplicity and performance in mind. It enables users to store, retrieve, and manage expenses efficiently while maintaining a clean and modular architecture.

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✨ Features

• 🧾 Create and store expenses
• 📊 Retrieve all expenses via API
• ⚡ Fast and async-ready with FastAPI
• 🗄️ SQLite database (auto-created)
• 🧩 Clean modular structure (routes, models, schemas)
• 📱 Supports Android Emulator & real devices
• 🔍 Interactive API testing with Swagger UI

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🛠️ Tech Stack

• FastAPI – API framework
• Uvicorn – ASGI server
• SQLAlchemy – ORM for database
• SQLite – Lightweight database
• Pydantic – Data validation

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📁 Project Structure

expense_backend/
├── main.py              # App entry point
├── database.py          # DB connection setup
├── models.py            # SQLAlchemy models
├── schemas.py           # Pydantic schemas
├── crud.py              # DB operations
├── requirements.txt     # Dependencies
└── routes/
    └── expense_routes.py  # API routes

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⚙️ Requirements

• Python 3.10+
• pip

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🚀 Quick Start

1️⃣ Create Virtual Environment

python -m venv venv
venv\Scripts\activate

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2️⃣ Install Dependencies

pip install -r requirements.txt

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3️⃣ Run Server

uvicorn main:app --host 0.0.0.0 --port 8000 --reload

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4️⃣ Access API

• 🌐 Base URL: http://127.0.0.1:8000
• 📘 Swagger Docs: http://127.0.0.1:8000/docs
• 📕 ReDoc: http://127.0.0.1:8000/redoc

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📡 API Endpoints

🔹 Health Check

GET /

{
  "message": "Expense Tracker API running"
}

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🔹 Create Expense

POST /expenses/

{
  "title": "Lunch",
  "amount": 150,
  "category": "Food"
}

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🔹 Get All Expenses

GET /expenses/

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🔗 Flutter Integration

Use the correct base URL depending on your device:

Platform	Base URL
Android Emulator	http://10.0.2.2:8000
iOS Simulator	http://127.0.0.1:8000
Real Device (Wi-Fi)	http://YOUR_IP:8000

Example

static const String baseUrl = "http://192.168.31.37:8000";

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🗄️ Database

• Uses SQLite
• Database file is auto-created
• Table: expenses

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🔄 Example Workflow

Flutter App → POST /expenses/ → Backend → Save to DB
Flutter App → GET /expenses/ → Backend → Return data → UI update

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🧪 Testing API

Use Swagger UI:

👉 http://127.0.0.1:8000/docs

• Try POST request
• Then GET to verify data

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⚠️ Troubleshooting

❌ Cannot connect from phone

✔ Ensure same Wi-Fi ✔ Use correct IP (192.168.x.x) ✔ Run server with 0.0.0.0

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❌ Connection refused

✔ Backend not running ✔ Wrong port or IP

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❌ Requests blocked

✔ Allow Python in Windows Firewall

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📌 Notes

• Database is automatically initialized on startup
• Simple structure makes it easy to scale
• Ready for future upgrades (auth, cloud deployment, etc.)

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🚀 Future Improvements

• 🔐 User Authentication (JWT)
• ☁️ Cloud Deployment (Render / Railway)
• 🔄 Real-time updates (WebSockets)
• 📊 Advanced analytics APIs
• 📁 Category-wise filtering

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👨‍💻 Author

Built with ❤️ for learning and real-world application development.

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⭐ Support

If you like this project:

⭐ Star this repo 🍴 Fork it 📢 Share it

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📬 Contact

Feel free to connect or ask questions!