Path operation dependencies in FastAPI - Mini Project: Build & Apply

Using Path Operation Dependencies in FastAPI

📖 Scenario: You are building a simple FastAPI app that manages user profiles. You want to reuse a common dependency that provides a fake current user object for multiple path operations.

🎯 Goal: Create a FastAPI app with a dependency function called get_current_user that returns a dictionary with user info. Use this dependency in two path operations: one to get the current user's profile and another to get the current user's items.

📋 What You'll Learn

Create a FastAPI app instance called app

Define a dependency function called get_current_user that returns {'username': 'alice'}

Use Depends(get_current_user) in two path operations: /users/me and /users/me/items

Each path operation should accept a parameter called current_user that receives the dependency result

💡 Why This Matters

🌍 Real World

Path operation dependencies help you reuse common logic like authentication or database sessions across many API endpoints without repeating code.

💼 Career

Understanding dependencies in FastAPI is essential for building clean, maintainable, and secure web APIs in professional backend development.

1

Create the FastAPI app and dependency function

Create a FastAPI app instance called app and define a dependency function called get_current_user that returns the dictionary {'username': 'alice'}.

FastAPI

from fastapi import FastAPI, Depends

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

Need a hint?

Use app = FastAPI() to create the app. Define a function get_current_user that returns the dictionary {'username': 'alice'}.

2

Add the first path operation using the dependency

Add a GET path operation at /users/me that uses Depends(get_current_user) to get the current user. The function should accept a parameter called current_user and return it.

FastAPI

from fastapi import FastAPI, Depends

app = FastAPI()

def get_current_user():
    return {'username': 'alice'}

# Add GET path operation /users/me using Depends(get_current_user)
# Your code here

Need a hint?

Use @app.get('/users/me') decorator. Define a function with parameter current_user: dict = Depends(get_current_user) and return current_user.

3

Add the second path operation using the same dependency

Add a GET path operation at /users/me/items that also uses Depends(get_current_user). The function should accept a parameter called current_user and return a dictionary with a key items and value as a list containing the string "item1".

FastAPI

from fastapi import FastAPI, Depends

app = FastAPI()

def get_current_user():
    return {'username': 'alice'}

@app.get('/users/me')
def read_current_user(current_user: dict = Depends(get_current_user)):
    return current_user

# Add GET path operation /users/me/items using Depends(get_current_user)
# Your code here

Need a hint?

Use @app.get('/users/me/items') decorator. Define a function with parameter current_user: dict = Depends(get_current_user) and return {'items': ['item1']}.

4

Add type hints and import Depends correctly

Ensure the Depends function is imported from fastapi and that both path operation functions have the parameter current_user typed as dict with = Depends(get_current_user).

FastAPI

from fastapi import FastAPI, Depends

app = FastAPI()

def get_current_user():
    return {'username': 'alice'}

@app.get('/users/me')
def read_current_user(current_user: dict = Depends(get_current_user)):
    return current_user

@app.get('/users/me/items')
def read_own_items(current_user: dict = Depends(get_current_user)):
    return {'items': ['item1']}

# Verify imports and type hints
# Your code here

Need a hint?

Check that Depends is imported from fastapi and used as a default value with type hint dict for current_user in both functions.