FastAPI + SQLAlchemy example

This example shows how to use Dependency Injector with FastAPI and SQLAlchemy.

The source code is available on the Github.

Thanks to @ShvetsovYura for providing initial example: FastAPI_DI_SqlAlchemy.

Application structure

Application has next structure:

./
├── webapp/
│   ├── __init__.py
│   ├── application.py
│   ├── containers.py
│   ├── database.py
│   ├── endpoints.py
│   ├── models.py
│   ├── repositories.py
│   ├── services.py
│   └── tests.py
├── config.yml
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

Application factory

Application factory creates container, wires it with the endpoints module, creates FastAPI app, and setup routes.

Application factory also creates database if it does not exist.

Listing of webapp/application.py:

"""Application module."""

from fastapi import FastAPI

from .containers import Container
from . import endpoints


def create_app() -> FastAPI:
    container = Container()
    container.config.from_yaml('config.yml')
    container.wire(modules=[endpoints])

    db = container.db()
    db.create_database()

    app = FastAPI()
    app.container = container
    app.include_router(endpoints.router)
    return app


app = create_app()

Endpoints

Module endpoints contains example endpoints. Endpoints have a dependency on user service. User service is injected using Wiring feature. See webapp/endpoints.py:

"""Endpoints module."""

from fastapi import APIRouter, Depends, Response, status
from dependency_injector.wiring import inject, Provide

from .containers import Container
from .services import UserService
from .repositories import NotFoundError

router = APIRouter()


@router.get('/users')
@inject
def get_list(
        user_service: UserService = Depends(Provide[Container.user_service]),
):
    return user_service.get_users()


@router.get('/users/{user_id}')
@inject
def get_by_id(
        user_id: int,
        user_service: UserService = Depends(Provide[Container.user_service]),
):
    try:
        return user_service.get_user_by_id(user_id)
    except NotFoundError:
        return Response(status_code=status.HTTP_404_NOT_FOUND)


@router.post('/users', status_code=status.HTTP_201_CREATED)
@inject
def add(
        user_service: UserService = Depends(Provide[Container.user_service]),
):
    return user_service.create_user()


@router.delete('/users/{user_id}', status_code=status.HTTP_204_NO_CONTENT)
@inject
def remove(
        user_id: int,
        user_service: UserService = Depends(Provide[Container.user_service]),
):
    try:
        user_service.delete_user_by_id(user_id)
    except NotFoundError:
        return Response(status_code=status.HTTP_404_NOT_FOUND)
    else:
        return Response(status_code=status.HTTP_204_NO_CONTENT)


@router.get('/status')
def get_status():
    return {'status': 'OK'}

Container

Declarative container wires example user service, user repository, and utility database class. See webapp/containers.py:

"""Containers module."""

from dependency_injector import containers, providers

from .database import Database
from .repositories import UserRepository
from .services import UserService


class Container(containers.DeclarativeContainer):

    config = providers.Configuration()

    db = providers.Singleton(Database, db_url=config.db.url)

    user_repository = providers.Factory(
        UserRepository,
        session_factory=db.provided.session,
    )

    user_service = providers.Factory(
        UserService,
        user_repository=user_repository,
    )

Services

Module services contains example user service. See webapp/services.py:

"""Services module."""

from uuid import uuid4
from typing import Iterator

from .repositories import UserRepository
from .models import User


class UserService:

    def __init__(self, user_repository: UserRepository) -> None:
        self._repository: UserRepository = user_repository

    def get_users(self) -> Iterator[User]:
        return self._repository.get_all()

    def get_user_by_id(self, user_id: int) -> User:
        return self._repository.get_by_id(user_id)

    def create_user(self) -> User:
        uid = uuid4()
        return self._repository.add(email=f'{uid}@email.com', password='pwd')

    def delete_user_by_id(self, user_id: int) -> None:
        return self._repository.delete_by_id(user_id)

Repositories

Module repositories contains example user repository. See webapp/repositories.py:

"""Repositories module."""

from contextlib import AbstractContextManager
from typing import Callable, Iterator

from sqlalchemy.orm import Session

from .models import User


class UserRepository:

    def __init__(self, session_factory: Callable[..., AbstractContextManager[Session]]) -> None:
        self.session_factory = session_factory

    def get_all(self) -> Iterator[User]:
        with self.session_factory() as session:
            return session.query(User).all()

    def get_by_id(self, user_id: int) -> User:
        with self.session_factory() as session:
            user = session.query(User).filter(User.id == user_id).first()
            if not user:
                raise UserNotFoundError(user_id)
            return user

    def add(self, email: str, password: str, is_active: bool = True) -> User:
        with self.session_factory() as session:
            user = User(email=email, hashed_password=password, is_active=is_active)
            session.add(user)
            session.commit()
            session.refresh(user)
            return user

    def delete_by_id(self, user_id: int) -> None:
        with self.session_factory() as session:
            entity: User = session.query(User).filter(User.id == user_id).first()
            if not entity:
                raise UserNotFoundError(user_id)
            session.delete(entity)
            session.commit()


class NotFoundError(Exception):

    entity_name: str

    def __init__(self, entity_id):
        super().__init__(f'{self.entity_name} not found, id: {entity_id}')


class UserNotFoundError(NotFoundError):

    entity_name: str = 'User'

Models

Module models contains example SQLAlchemy user model. See webapp/models.py:

"""Models module."""

from sqlalchemy import Column, String, Boolean, Integer

from .database import Base


class User(Base):

    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    email = Column(String, unique=True)
    hashed_password = Column(String)
    is_active = Column(Boolean, default=True)

    def __repr__(self):
        return f'<User(id="{self.id}", ' \
               f'email="{self.email}", ' \
               f'hashed_password="{self.hashed_password}", ' \
               f'is_active="{self.is_active}")>'

Database

Module database defines declarative base and utility class with engine and session factory. See webapp/database.py:

"""Database module."""

from contextlib import contextmanager, AbstractContextManager
from typing import Callable
import logging

from sqlalchemy import create_engine, orm
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session

logger = logging.getLogger(__name__)

Base = declarative_base()


class Database:

    def __init__(self, db_url: str) -> None:
        self._engine = create_engine(db_url, echo=True)
        self._session_factory = orm.scoped_session(
            orm.sessionmaker(
                autocommit=False,
                autoflush=False,
                bind=self._engine,
            ),
        )

    def create_database(self) -> None:
        Base.metadata.create_all(self._engine)

    @contextmanager
    def session(self) -> Callable[..., AbstractContextManager[Session]]:
        session: Session = self._session_factory()
        try:
            yield session
        except Exception:
            logger.exception('Session rollback because of exception')
            session.rollback()
            raise
        finally:
            session.close()

Tests

Tests use Provider overriding feature to replace repository with a mock. See webapp/tests.py:

"""Tests module."""

from unittest import mock

import pytest
from fastapi.testclient import TestClient

from .repositories import UserRepository, UserNotFoundError
from .models import User
from .application import app


@pytest.fixture
def client():
    yield TestClient(app)


def test_get_list(client):
    repository_mock = mock.Mock(spec=UserRepository)
    repository_mock.get_all.return_value = [
        User(id=1, email='test1@email.com', hashed_password='pwd', is_active=True),
        User(id=2, email='test2@email.com', hashed_password='pwd', is_active=False),
    ]

    with app.container.user_repository.override(repository_mock):
        response = client.get('/users')

    assert response.status_code == 200
    data = response.json()
    assert data == [
        {'id': 1, 'email': 'test1@email.com', 'hashed_password': 'pwd', 'is_active': True},
        {'id': 2, 'email': 'test2@email.com', 'hashed_password': 'pwd', 'is_active': False},
    ]


def test_get_by_id(client):
    repository_mock = mock.Mock(spec=UserRepository)
    repository_mock.get_by_id.return_value = User(
        id=1,
        email='xyz@email.com',
        hashed_password='pwd',
        is_active=True,
    )

    with app.container.user_repository.override(repository_mock):
        response = client.get('/users/1')

    assert response.status_code == 200
    data = response.json()
    assert data == {'id': 1, 'email': 'xyz@email.com', 'hashed_password': 'pwd', 'is_active': True}
    repository_mock.get_by_id.assert_called_once_with(1)


def test_get_by_id_404(client):
    repository_mock = mock.Mock(spec=UserRepository)
    repository_mock.get_by_id.side_effect = UserNotFoundError(1)

    with app.container.user_repository.override(repository_mock):
        response = client.get('/users/1')

    assert response.status_code == 404


@mock.patch('webapp.services.uuid4', return_value='xyz')
def test_add(_, client):
    repository_mock = mock.Mock(spec=UserRepository)
    repository_mock.add.return_value = User(
        id=1,
        email='xyz@email.com',
        hashed_password='pwd',
        is_active=True,
    )

    with app.container.user_repository.override(repository_mock):
        response = client.post('/users')

    assert response.status_code == 201
    data = response.json()
    assert data == {'id': 1, 'email': 'xyz@email.com', 'hashed_password': 'pwd', 'is_active': True}
    repository_mock.add.assert_called_once_with(email='xyz@email.com', password='pwd')


def test_remove(client):
    repository_mock = mock.Mock(spec=UserRepository)

    with app.container.user_repository.override(repository_mock):
        response = client.delete('/users/1')

    assert response.status_code == 204
    repository_mock.delete_by_id.assert_called_once_with(1)


def test_remove_404(client):
    repository_mock = mock.Mock(spec=UserRepository)
    repository_mock.delete_by_id.side_effect = UserNotFoundError(1)

    with app.container.user_repository.override(repository_mock):
        response = client.delete('/users/1')

    assert response.status_code == 404


def test_status(client):
    response = client.get('/status')
    assert response.status_code == 200
    data = response.json()
    assert data == {'status': 'OK'}

Sources

The source code is available on the Github.