Shared dependencies across routers in FastAPI - Mini Project: Build & Apply

Shared dependencies across routers in FastAPI

📖 Scenario: You are building a web API for a simple book store. You want to organize your API into separate routers for books and authors. Both routers need to check a shared dependency that simulates user authentication.

🎯 Goal: Create two routers, books_router and authors_router, each with one route. Add a shared dependency get_current_user to both routers so that the user is authenticated before accessing any route.

📋 What You'll Learn

Create a dependency function called get_current_user that returns a string 'user123'.

Create a FastAPI app instance called app.

Create two routers: books_router and authors_router.

Add the get_current_user dependency to both routers using the dependencies parameter.

Add one route /books/ to books_router that returns a JSON with key 'message' and value 'Books list'.

Add one route /authors/ to authors_router that returns a JSON with key 'message' and value 'Authors list'.

Include both routers in the main app with prefixes /books and /authors respectively.

💡 Why This Matters

🌍 Real World

In real web APIs, shared dependencies like authentication or database sessions are used across multiple routers to keep code clean and secure.

💼 Career

Understanding how to share dependencies across routers is essential for building scalable and maintainable FastAPI applications in professional backend development.

1

Create the shared dependency function

Create a function called get_current_user that returns the string 'user123'.

FastAPI

# Your code here

Need a hint?

This function simulates user authentication by returning a fixed user ID.

2

Create FastAPI app and routers with shared dependency

Import FastAPI and APIRouter from fastapi. Create a FastAPI app called app. Create two routers called books_router and authors_router with the shared dependency get_current_user added using the dependencies parameter.

FastAPI

def get_current_user():
    return 'user123'

# Your code here

Need a hint?

Use Depends(get_current_user) inside the dependencies list when creating each router.

3

Add routes to routers

Add a GET route / to books_router that returns {'message': 'Books list'}. Add a GET route / to authors_router that returns {'message': 'Authors list'}.

FastAPI

from fastapi import FastAPI, APIRouter, Depends

def get_current_user():
    return 'user123'

app = FastAPI()

books_router = APIRouter(dependencies=[Depends(get_current_user)])
authors_router = APIRouter(dependencies=[Depends(get_current_user)])

# Your code here

Need a hint?

Use the @router.get('/') decorator and define functions that return the required dictionaries.

4

Include routers in the main app

Include books_router in app with prefix /books. Include authors_router in app with prefix /authors.

FastAPI

from fastapi import FastAPI, APIRouter, Depends

def get_current_user():
    return 'user123'

app = FastAPI()

books_router = APIRouter(dependencies=[Depends(get_current_user)])
authors_router = APIRouter(dependencies=[Depends(get_current_user)])

@books_router.get('/')
def read_books():
    return {'message': 'Books list'}

@authors_router.get('/')
def read_authors():
    return {'message': 'Authors list'}

# Your code here

Need a hint?

Use app.include_router() with the correct router and prefix.