Class-based dependencies in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a class-based dependency in FastAPI?

A class-based dependency is a Python class used to define reusable logic that FastAPI can inject into path operations. It allows grouping related code and state in one place.

beginner

How do you make a class usable as a dependency in FastAPI?

You define a __call__ method inside the class. FastAPI treats instances of this class as callable dependencies.

intermediate

Why use class-based dependencies instead of functions in FastAPI?

Class-based dependencies help organize related logic and state together, making code cleaner and easier to maintain, especially when you need to share data or setup across multiple calls.

intermediate

How does FastAPI handle the lifecycle of class-based dependencies?

FastAPI creates a new instance of the class for each request by default, calling its __call__ method to resolve the dependency.

advanced

Can class-based dependencies have their own dependencies in FastAPI?

Yes, you can declare dependencies inside the __init__ method or __call__ method, allowing nested dependency injection.

What special method must a class have to be used as a FastAPI dependency?

A __str__

B __call__

C __init__

D __repr__

FastAPI uses the __call__ method to treat the class instance as a callable dependency.

How does FastAPI create instances of class-based dependencies by default?

A One instance per request

B It does not create instances automatically

C One instance per application startup

D One instance shared across all requests

FastAPI creates a new instance of the class for each request to keep dependencies isolated.

Where can you declare nested dependencies inside a class-based dependency?

A In both __init__ and __call__ methods

B Only in __init__ method

C Only in __call__ method

D Nested dependencies are not supported

You can declare nested dependencies in both __init__ and __call__ methods for flexibility.

What is a main benefit of using class-based dependencies?

A They avoid using async functions

B They run faster than function dependencies

C They require less code

D They allow grouping related logic and state

Class-based dependencies help organize related code and state together for cleaner design.

Which FastAPI feature allows injecting class-based dependencies into path operations?

A Request

B Response

C Depends

D Middleware

The Depends function is used to declare dependencies, including class-based ones.

Explain how to create and use a class-based dependency in FastAPI.

Think about how FastAPI treats callable classes as dependencies.

Describe the advantages of using class-based dependencies over function dependencies in FastAPI.

Consider how grouping logic and state helps in bigger projects.