Depends function basics in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Depends function in FastAPI?

Depends is used to declare dependencies for path operation functions. It helps FastAPI know what extra data or logic to run before your endpoint code.

beginner

How do you use Depends to inject a dependency into a FastAPI path operation?

You add a function parameter with Depends(your_dependency_function). FastAPI calls that function and passes its result to your endpoint.

intermediate

Can Depends be used to share common logic like authentication or database sessions?

Yes! Depends is perfect for reusing code like checking user login or creating a database session before running your endpoint.

intermediate

What happens if a dependency function used with Depends raises an exception?

FastAPI stops running the endpoint and returns the error response immediately. This helps handle errors early, like unauthorized access.

advanced

Is it possible to have nested dependencies with Depends in FastAPI?

Yes, a dependency function can itself use Depends to call other dependencies. FastAPI resolves them all automatically.

What does Depends do in FastAPI?

A Defines a new API route

B Declares a dependency to be injected into a path operation

C Handles HTTP requests directly

D Creates database tables automatically

Depends tells FastAPI to run a function and pass its result as a parameter to your endpoint.

How do you tell FastAPI to use a dependency function named get_db?

A Add get_db() inside the endpoint code

B Import get_db but do not call it

C Use Depends(get_db) as a parameter in the endpoint function

D Call get_db in the main app startup

You add a parameter with Depends(get_db) so FastAPI calls get_db and passes its result.

What happens if a Depends dependency raises an HTTPException?

A FastAPI returns the error response immediately

B The endpoint runs normally

C The exception is ignored

D The server crashes

FastAPI stops the endpoint and returns the error response when a dependency raises HTTPException.

Can a dependency function use Depends to call another dependency?

A Yes, nested dependencies are supported

B Only if you use global variables

C No, dependencies cannot be nested

D Only in class-based views

FastAPI supports nested dependencies where one dependency calls another using Depends.

Which of these is a common use case for Depends?

A Creating database tables

B Defining HTML templates

C Writing CSS styles

D Sharing authentication logic

Depends is often used to share logic like authentication or database sessions across endpoints.

Explain how Depends works in FastAPI and why it is useful.

Think about how you can share common setup code for many endpoints.

Describe a scenario where nested dependencies with Depends would be helpful.

Consider when one setup step needs another to work first.