Dependecies overrides are not taken into account into the apenapi document

[lmignon]

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Example Code

from fastapi import Depends, FastAPI, Header
from fastapi.security import OAuth2PasswordBearer
from fastapi.testclient import TestClient

app = FastAPI()


def get_user_id() -> int:
    pass


def get_user(user_id=Depends(get_user_id)) -> str:
    return f"{user_id}"


oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")


def get_user_id_from_auth_override(token: str = Depends(oauth2_scheme)) -> int:
    return 1


def get_user_id_from_header_override(user_id: int = Header()) -> int:
    return user_id


@app.get("/user")
def read_user(
    user: str = Depends(get_user),
):
    return user


client = TestClient(app)


override_with_security_schema = {
    "components": {
        "securitySchemes": {
            "OAuth2PasswordBearer": {
                "flows": {"password": {"scopes": {}, "tokenUrl": "token"}},
                "type": "oauth2",
            }
        }
    },
    "info": {"title": "FastAPI", "version": "0.1.0"},
    "openapi": "3.0.2",
    "paths": {
        "/user": {
            "get": {
                "operationId": "read_user_user_get",
                "responses": {
                    "200": {
                        "content": {"application/json": {"schema": {}}},
                        "description": "Successful " "Response",
                    }
                },
                "security": [{"OAuth2PasswordBearer": []}],
                "summary": "Read User",
            }
        }
    },
}

app.dependency_overrides[get_user_id] = get_user_id_from_auth_override
app.openapi_schema = None
response = client.get("/openapi.json")
assert response.status_code == 200, response.text
assert response.json() == override_with_security_schema

Description

DI is a great feature. We use it to develop reusable APIs routers packaged in different python modules. Depending of the customer requirements, the routers are assembled into a dedicated App .Each service requiring to get the user information declares a Depends on a generic method get_user. The dependencies_override functionality is then used to define the concrete implementation of this method when the application is assembled according to the customer needs. If the override work as expected in such a case, unfortunately the overrides are not taken into account into the openapi documentation.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.85.0

Python Version

3.10

Additional Context

No response

[lmignon]

Any news about this proposal? It's very useful and allows to build reusable routers into different app....

[YuriiMotov]

I think it works as it should work.
You shouldn't use dependencies_override to change openapi schema. It's only for mocking some dependencies in tests

[lmignon]

@YuriiMotov
We don't use-it to only to change the schema but to be able to create reusable components. With this approach we design for example a library providing a set of routes which depends on the authenticated user and when these routes are mounted into the app, we provide the real implementation as an override of the method specified into the depends declaration. It's a kind of dependency injection that allows you to reuse the same library into different contexts. It's very very useful and works in production for years now. The only issue is that the overrides are not taken into account when the openapi schema is generated from the final app. Can you reconsider your response or do I need to find my proper way to do it? I think that this use case is an advanced and powerful feature provided by fastapi.

[lmignon]

The related PR is #5452

[YuriiMotov]

My opinion is that this is a misuse of dependencies_override mechanism.

This is for testing, to replace expensive dependencies with testing versions.

Source: https://fastapi.tiangolo.com/reference/fastapi/#fastapi.FastAPI.dependency_overrides

It's intended to be used for overriding dependencies in tests. I don't see a point in testing openapi schema with overridden dependencies.

If think you'd better describe your use case with examples and open new discussion with feature request.
If it has wide community support, FastAPI team will take a look and probably accept this feature request

[YuriiMotov]

Good explanation of the idea in this comment: #5452 (comment) (just added the link for people who will read this)