FastAPI top-level dependencies

#python #news #tutorial

This article lives in:

Intro

FastAPI version 0.62.0 comes with global dependencies that you can apply to a whole application.

As well as top-level dependencies, tags, and other parameters for APIRouters, that before were available only on app.include_router().

This makes it easier to put configurations and dependencies (e.g. for authentication) related to a group of path operations more closely together. 🔒

Let's start by checking APIRouter...

Include a router

Imagine you had a file users.py with:

from fastapi import APIRouter

router = APIRouter()


@router.get("/users/")
def read_users():
    return ["rick", "morty"]

And now let's say you want to include it in the main.py file with:

from fastapi import FastAPI, Depends
from . import users
from .dependencies import get_query_token

app = FastAPI()

app.include_router(
    users.router,
    tags=["users"],
    dependencies=[Depends(get_query_token)]
)


@app.get("/")
def main():
    return {"message": "Hello World"}

In this example, you are applying the tag users to all the path operations in users.py. And you are also applying the dependency get_query_token to all of them.

This works, and it was the only/main way to do it up to version 0.62.0.

But what is not so great about it is that the tag and the dependency are mainly related to users.py, not to main.py. But that code had to live in main.py, instead of being closer to what it is related to.

`APIRouter` top-level dependencies and tags

Now, with FastAPI version 0.62.0, you can declare top-level dependencies, tags, and others in the APIRouter directly.

So, the new router.py can now look like:

from fastapi import APIRouter, Depends
from .dependencies import get_query_token

router = APIRouter(
    tags=["users"],
    dependencies=[Depends(get_query_token)]
)


@router.get("/users/")
def read_users():
    return ["rick", "morty"]

...notice the tags and dependencies in the APIRouter, they can now live closer to their related code! 🎉

And the main.py would be simply:

from fastapi import FastAPI
from . import users

app = FastAPI()

app.include_router(
    users.router,
)


@app.get("/")
def main():
    return {"message": "Hello World"}

Global dependencies

In the same way, you can now also declare dependencies that apply to all the path operations in the FastAPI application:

from fastapi import FastAPI, Depends
from .dependencies import get_query_token

app = FastAPI(
    dependencies=[Depends(get_query_token)]
)

@app.get("/")
def main():
    return {"message": "Hello World"}

Tips

Some tips to adopt a convention:

By default, set all those configs in APIRouter().
Try to only set them in app.include_router() when you want to override some defaults that can't (or shouldn't) be set in APIRouter directly.
Set them in FastAPI() only when you want them to apply to everything, e.g. some default authentication for a simple app.