Global dependencies in FastAPI - Mini Project: Build & Apply

Using Global Dependencies in FastAPI

📖 Scenario: You are building a simple web API with FastAPI. You want to reuse a common dependency across multiple routes to avoid repeating code.

🎯 Goal: Create a FastAPI app that uses a global dependency to provide a fixed API key to all routes.

📋 What You'll Learn

Create a dependency function that returns the string 'mysecretapikey'.

Add this dependency globally to the FastAPI app.

Create two routes: /items/ and /users/ that receive the API key from the global dependency.

Return a JSON response from each route showing the API key.

💡 Why This Matters

🌍 Real World

Global dependencies are useful when you want to apply common logic like authentication, logging, or configuration to many routes without repeating code.

💼 Career

Understanding global dependencies in FastAPI is important for backend developers building scalable and maintainable APIs.

1

Create the FastAPI app and dependency function

Create a FastAPI app called app and define a dependency function called get_api_key that returns the string 'mysecretapikey'.

FastAPI

# Create the FastAPI app and the dependency function get_api_key
# Your code here

Need a hint?

Import FastAPI and create an instance named app. Define a function get_api_key that returns the fixed string.

2

Add the global dependency to the FastAPI app

Add the global dependency get_api_key to the FastAPI app app using the dependencies parameter in the app constructor.

FastAPI

from fastapi import FastAPI, Depends

def get_api_key():
    return 'mysecretapikey'

# Add the global dependency get_api_key to the app
app = FastAPI(dependencies=[Depends(get_api_key)])

# Your code here

Need a hint?

Use Depends(get_api_key) inside the dependencies list when creating the app.

3

Create the /items/ route using the global dependency

Create a route /items/ using @app.get that accepts a parameter api_key of type str with a default value from Depends(get_api_key). Return a dictionary with the key 'api_key' and the value api_key.

FastAPI

from fastapi import FastAPI, Depends

def get_api_key():
    return 'mysecretapikey'

app = FastAPI(dependencies=[Depends(get_api_key)])

# Create /items/ route here
# Your code here

Need a hint?

Define an async function with the route decorator. Use api_key: str = Depends(get_api_key) as a parameter.

4

Create the /users/ route using the global dependency

Create a route /users/ using @app.get that accepts a parameter api_key of type str with a default value from Depends(get_api_key). Return a dictionary with the key 'api_key' and the value api_key.

FastAPI

from fastapi import FastAPI, Depends

def get_api_key():
    return 'mysecretapikey'

app = FastAPI(dependencies=[Depends(get_api_key)])

@app.get('/items/')
async def read_items(api_key: str = Depends(get_api_key)):
    return {'api_key': api_key}

# Create /users/ route here
# Your code here

Need a hint?

Define another async function with the route decorator for /users/. Use the same dependency parameter.