modern-di integration for FastAPI.
Full guide: FastAPI integration docs
Usage example: fastapi-sqlalchemy-template
Installation
uv add modern-di-fastapi # or: pip install modern-di-fastapi
Usage
setup_di stores the container on the app and opens and closes it with the app lifespan. The container opens before your lifespan's startup code and closes after its shutdown code, so both can resolve APP-scoped dependencies. FromDI resolves a provider (or type) into a route parameter. It builds the per-connection child container on demand through Depends(build_di_container), so only routes that use FromDI get one.
import dataclasses
import fastapi
from modern_di import Container, Group, Scope, providers
from modern_di_fastapi import FromDI, setup_di
@dataclasses.dataclass(kw_only=True)
class Settings:
debug: bool = True
@dataclasses.dataclass(kw_only=True)
class UserService:
settings: Settings # auto-injected by type
class Dependencies(Group):
settings = providers.Factory(scope=Scope.APP, creator=Settings)
user_service = providers.Factory(scope=Scope.REQUEST, creator=UserService)
app = fastapi.FastAPI()
container = Container(groups=[Dependencies])
setup_di(app, container)
container.validate() # optional fail-fast; must come after setup_di registers its providers
@app.get("/")
async def index(user_service: UserService = FromDI(Dependencies.user_service)) -> dict[str, bool]:
return {"debug": user_service.settings.debug}
The framework Request / WebSocket are resolvable within DI via the pre-built fastapi_request_provider / fastapi_websocket_provider context providers.
An app mounted under another with app.mount can call setup_di with its own container, and its routes resolve from that container. Starlette runs only the outermost app's lifespan, so the outer app's lifespan also opens and closes the root container of every mounted app that called setup_di, including apps under Host routes, apps mounted with Mount(..., middleware=[...]), and apps mounted more than one level deep. It looks for them at startup, so mounts added after setup_di are included. Each container is opened once at startup, before your lifespan code, and closed once at shutdown, after it. The mounted app's own lifespan function still does not run. A mounted app whose setup_di was called with manage_lifespan=False keeps its root out of this. The flag covers only the container of the app it is passed to, and a mounted app's own setup_di call decides for its container: an outer app with manage_lifespan=False still opens and closes the containers of mounted apps that kept the default.
Sharing a container
Pass manage_lifespan=False when something else owns the root container, for example one container shared by several apps. setup_di then never opens or closes the root, and you do. It still registers its providers and still opens and closes a child container for each connection.
import uvicorn
container = Container(groups=[Dependencies])
setup_di(app, container, manage_lifespan=False)
async def main() -> None:
async with container:
await uvicorn.Server(uvicorn.Config(app)).serve()
API
| Symbol | Description |
|---|---|
setup_di(app, container, *, manage_lifespan=True) |
Stores the container on app.state and composes the container's open/close into the app lifespan (opening it before any existing lifespan= starts and closing it after that lifespan's shutdown code). With manage_lifespan=False the lifespan leaves the root alone and you open and close it |
FromDI(dependency, *, use_cache=True) |
FastAPI Depends that resolves a provider (or type) from the per-connection child container. Raises RuntimeError naming setup_di when a request reaches it without setup_di called |
fetch_di_container(app) |
Returns the app-scoped container from app.state. Raises RuntimeError naming setup_di when called without setup_di called |
build_di_container(connection) |
FastAPI Depends callable that yields the per-connection child container: REQUEST scope for an HTTP request, SESSION scope for a WebSocket |
fastapi_request_provider |
ContextProvider for the current fastapi.Request (REQUEST scope) |
fastapi_websocket_provider |
ContextProvider for the current fastapi.WebSocket (SESSION scope) |
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Part of modern-python
Built on modern-di, a dependency-injection framework with an IoC container and scopes.
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Release files for modern-di-fastapi 4.2.1
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