API versioning strategies in FastAPI - Mini Project: Build & Apply

API Versioning Strategies with FastAPI

📖 Scenario: You are building a simple web API for a bookstore. Over time, you want to add new features without breaking existing clients. To do this, you will create two versions of the API endpoints using FastAPI.

🎯 Goal: Build a FastAPI application that supports two API versions: v1 and v2. Each version will have a /books endpoint returning different data formats. You will learn how to organize routes to handle versioning cleanly.

📋 What You'll Learn

Create a FastAPI app with two routers for versions v1 and v2

Define a /books GET endpoint in each version router

Return a list of books with different fields in v1 and v2

Mount the routers under /api/v1 and /api/v2 paths

💡 Why This Matters

🌍 Real World

APIs often need to evolve without breaking existing clients. Versioning helps manage changes safely.

💼 Career

Understanding API versioning is essential for backend developers working on web services and microservices.

1

Create initial book data

Create a list called books with two dictionaries. Each dictionary should have keys id and title with these exact values: {'id': 1, 'title': '1984'} and {'id': 2, 'title': 'Brave New World'}.

FastAPI

# Create the books list with two dictionaries
# Your code here

Need a hint?

Use a list with two dictionaries exactly as shown.

2

Set up FastAPI app and routers

Import FastAPI and APIRouter from fastapi. Create a FastAPI app called app. Create two routers called router_v1 and router_v2 using APIRouter().

FastAPI

books = [
    {'id': 1, 'title': '1984'},
    {'id': 2, 'title': 'Brave New World'}
]

# Import FastAPI and APIRouter
# Create app and two routers
# Your code here

Need a hint?

Remember to import both FastAPI and APIRouter and create the app and routers with exact names.

3

Define versioned /books endpoints

Add a GET endpoint /books to router_v1 that returns the books list as is. Add a GET endpoint /books to router_v2 that returns a list of books with id, title, and a new key author with value 'Unknown' for each book.

FastAPI

from fastapi import FastAPI, APIRouter

books = [
    {'id': 1, 'title': '1984'},
    {'id': 2, 'title': 'Brave New World'}
]

app = FastAPI()
router_v1 = APIRouter()
router_v2 = APIRouter()

# Add GET /books to router_v1 returning books
# Add GET /books to router_v2 returning books with author='Unknown'
# Your code here

Need a hint?

Use list comprehension to add the author key in v2.

4

Mount routers with version prefixes

Mount router_v1 on /api/v1 and router_v2 on /api/v2 using app.include_router().

FastAPI

from fastapi import FastAPI, APIRouter

books = [
    {'id': 1, 'title': '1984'},
    {'id': 2, 'title': 'Brave New World'}
]

app = FastAPI()
router_v1 = APIRouter()
router_v2 = APIRouter()

@router_v1.get('/books')
async def get_books_v1():
    return books

@router_v2.get('/books')
async def get_books_v2():
    return [{**book, 'author': 'Unknown'} for book in books]

# Mount router_v1 on /api/v1
# Mount router_v2 on /api/v2
# Your code here

Need a hint?

Use app.include_router() with the prefix argument for versioning.