Global dependencies in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a global dependency in FastAPI?

A global dependency is a function or class that FastAPI runs for every request in an application or router, providing shared logic like authentication or database sessions.

beginner

How do you declare a global dependency in FastAPI?

You declare a global dependency by passing it to the 'dependencies' parameter of the FastAPI app or APIRouter, so it runs automatically for all routes inside.

intermediate

What is a practical example of a global dependency?

A common example is an authentication check that runs before every request to verify the user is logged in, so you don't repeat this check in every route.

intermediate

Can global dependencies return values to route functions in FastAPI?

Yes, global dependencies can return values that route functions receive as parameters, allowing shared data like user info or database sessions to be used inside routes.

intermediate

What happens if a global dependency raises an exception in FastAPI?

If a global dependency raises an exception, FastAPI stops processing the request and returns an error response, preventing the route handler from running.

How do you apply a global dependency to all routes in a FastAPI app?

A Pass the dependency to the 'dependencies' parameter when creating the FastAPI app

B Add the dependency inside each route function manually

C Use a middleware instead of dependencies

D Call the dependency inside the main function

Global dependencies are set by passing them to the 'dependencies' parameter of the FastAPI app or router, so they run automatically for all routes.

What is a benefit of using global dependencies in FastAPI?

A They make the app slower by adding extra steps

B They reduce repeated code by sharing logic across routes

C They replace the need for route functions

D They automatically generate HTML pages

Global dependencies help avoid repeating the same code in every route by running shared logic once for all routes.

Can global dependencies in FastAPI provide data to route handlers?

A Yes, they can return values that routes receive as parameters

B No, they only run code but cannot pass data

C Only if you use global variables

D Only if you use middleware

Global dependencies can return values that FastAPI injects into route function parameters for use inside the route.

Where else besides the FastAPI app can you set global dependencies?

A In the HTML templates

B Only in the main app

C In the database connection

D In APIRouter instances

You can set global dependencies on APIRouter objects to apply them to all routes within that router.

What happens if a global dependency raises an HTTPException?

A The exception is ignored

B The request continues normally

C FastAPI returns the error response immediately

D The server crashes

If a global dependency raises an HTTPException, FastAPI stops processing and returns the error response to the client.

Explain how to use global dependencies in FastAPI and why they are useful.

Think about code you want to run for every request without repeating it.

Describe what happens when a global dependency raises an error in FastAPI.

Consider how FastAPI handles exceptions in dependencies.