66-fastapi-versioning

66 - API Versioning

What It Does

Demonstrates how to structure a FastAPI application to support multiple API versions concurrently. When breaking changes must be made to an API (like restructuring the response JSON), creating a v2 router allows new clients to use the new features while legacy clients continue using v1 without breaking. Includes a unified frontend dashboard to visualize the difference between the two versions.

Project Structure

66-fastapi-versioning/
  main.py            # FastAPI Entry point
  api/
    v1/
      routes.py      # Legacy v1 endpoints
    v2/
      routes.py      # New v2 endpoints
  index.html         # Unified Frontend to compare v1 vs v2
  requirements.txt   # Dependencies
  README.md          # This file

Setup and Run

1. Install dependencies

pip install -r requirements.txt

2. Start the FastAPI Server

uvicorn main:app --reload

3. Open the Frontend

Open index.html directly in your browser to test calling /api/v1/users vs /api/v2/users.

Example Output

// GET /api/v1/users
{
  "version": "v1",
  "data": [{"id": 1, "name": "John Doe", "email": "john@example.com"}]
}

// GET /api/v2/users
{
  "version": "v2",
  "data": [{"id": 1, "first_name": "John", "last_name": "Doe", "email": "john@example.com", "is_active": true}]
}

Core Concepts

• APIRouter: FastAPIs method for breaking up large applications.
• Prefixes: Mapping routers to physical URL paths like prefix="/api/v1".
• Schema Evolution: Observing how data structures change (e.g., flattening a name into first_name and last_name) while maintaining backward compatibility.