[QUESTION] Dependency Injection - Inject child class

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Description

I there a way to specify to inject a child class instead of the class declared as a dependency ?

In my example I want to specify that all my endpoints must be authenticated, but I don’t want to have to specify how the authentication must be done at the endpoint declaration level.

I would like to be able to specify that when Auth is indicated as a dependency then BasicAuth must be injected.

This way changing the authentication medium would need to change a single configuration line and not all the endpoints.

Example Code

from starlette.requests import Request

class Auth:
    """
    Base class that all authenticator will extend
    """
    def __init__(self, request: Request):
        self.perform_authentication(request)

    def perform_authentication(self, request: Request):
        raise NotImplementedError()


class BasicAuth(Auth):
    def perform_authentication(self, request: Request):
        # Perform auth based on the HTTP Basic header


# I want my endpoint to be authenticated but I don't care about the way here
@app.get("/items/", dependencies=[Depends(Auth))
async def read_items():
    pass

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.67

Python Version

3.10

Additional Context

No response

[adriangb]

This is a normal use case for DI. What you want is to declare a dependency on an interface/abstraction and then bind a concrete implementation for deployment or testing. I think #3641 takes care of this use case since you can .bind(Auth, BasicAuth)

[Darkheir]

This is a normal use case for DI. What you want is to declare a dependency on an interface/abstraction and then bind a concrete implementation for deployment or testing. I think #3641 takes care of this use case since you can .bind(Auth, BasicAuth)

Yes this is typically what I would like ! From what I understood it is not possible as of now, but I will watch closely your PR 😃