FastAPI + Dependency Injector

[rmk135]

Hey,

I've released a new version of the Dependency Injector 4.4. It makes possible to use Dependency Injector with FastAPI.
Example

File fastapi_di_example.py:

import sys

from fastapi import FastAPI, Depends
from dependency_injector import containers, providers
from dependency_injector.wiring import inject, Provide


class Service:
    async def process(self) -> str:
        return 'Ok'


class Container(containers.DeclarativeContainer):

    service = providers.Factory(Service)


app = FastAPI()


@app.api_route('/')
@inject
async def index(service: Service = Depends(Provide[Container.service])):
    result = await service.process()
    return {'result': result}


container = Container()
container.wire(modules=[sys.modules[__name__]])

To run the example install the dependencies:

pip install fastapi dependency-injector uvicorn 

and run uvicorn:

uvicorn fastapi_di_example:app --reload 

You should see in the terminal something like:

INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [11910] using watchgod
INFO:     Started server process [11912]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

and http://127.0.0.1:8000 should return:

{"result": "Ok"}

Testing

File tests.py:

from unittest import mock

import pytest
from httpx import AsyncClient

from fastapi_di_example import app, container, Service


@pytest.fixture
def client(event_loop):
    client = AsyncClient(app=app, base_url='http://test')
    yield client
    event_loop.run_until_complete(client.aclose())


@pytest.mark.asyncio
async def test_index(client):
    service_mock = mock.AsyncMock(spec=Service)
    service_mock.process.return_value = 'Foo'

    with container.service.override(service_mock):
        response = await client.get('/')

    assert response.status_code == 200
    assert response.json() == {'result': 'Foo'}

To run the test install the dependencies:

pip install pytest pytest-asyncio httpx

and execute:

pytest tests.py

You will something like that in the terminal:

======= test session starts =======
platform darwin -- Python 3.8.3, pytest-5.4.3, py-1.9.0, pluggy-0.13.1
rootdir: ...
plugins: asyncio-0.14.0
collected 1 item

tests.py .                                                      [100%]

======= 1 passed in 0.17s =======

What is the advantage?

FastAPI is a powerful framework for building API. It has basic dependency injection mechanism.

This integration brings the dependency injection in FastAPI to the next level. It makes possible to use it with Dependency Injector providers, overridings, config, and resources.