fastapi-sqla

A highly opinionated SQLAlchemy extension for FastAPI:

• Setup using environment variables to connect on DB;
• fastapi_sqla.Base a declarative base class to reflect DB tables at startup;
• fastapi_sqla.Session a dependency to get an sqla session;
• fastapi_sqla.open_session a context manager to get an sqla session;
• fastapi_sqla.async_support.AsyncSession a dependency to get an async sqla session ;
• fastapi_sqla.async_support.open_session a context manager to get an async sqla session;
• Automated commit/rollback of sqla session at the end of request before returning response;
• Pagination utilities;
• Pytest fixtures;

Configuration

Environment variables:

The keys of interest in os.environ are prefixed with sqlalchemy_. Each matching key (after the prefix is stripped) is treated as though it were the corresponding keyword argument to sqlalchemy.create_engine call.

The only required key is sqlalchemy_url, which provides the database URL.

asyncio support using asyncpg

SQLAlchemy >= 1.4 supports asyncio. To enable asyncio support against a Postgres DB, install asyncpg:

pip install asyncpg

And define environment variable async_sqlalchemy_url with postgres+asyncpg scheme:

export async_sqlalchemy_url=postgresql+asyncpg://postgres@localhost

Setup the app:

import fastapi_sqla
from fastapi import FastAPI

app = FastAPI()
fastapi_sqla.setup(app)

SQLAlchemy

Adding a new entity class:

from fastapi_sqla import Base


class Entity(Base):
    __tablename__ = "table-name-in-db"

Getting an sqla session

Using dependency injection

Use FastAPI dependency injection to get a session as a parameter of a path operation function. SQLAlchemy session is committed before response is returned or rollbacked if any exception occurred:

from fastapi import APIRouter, Depends
from fastapi_sqla import Session
from fastapi_sqla.asyncio_support import AsyncSession

router = APIRouter()


@router.get("/example")
def example(session: Session = Depends()):
    return session.execute("SELECT now()").scalar()


@router.get("/async_example")
async def async_example(session: AsyncSession = Depends()):
    return await session.execute("SELECT now()").scalar()

Using a context manager

When needing a session outside of a path operation, like when using FastAPI background tasks, use fastapi_sqla.open_session context manager. SQLAlchemy session is committed when exiting context or rollbacked if any exception occurred:

from fastapi import APIRouter, BackgroundTasks
from fastapi_sqla import open_session
from fastapi_sqla import asyncio_support

router = APIRouter()


@router.get("/example")
def example(bg: BackgroundTasks):
    bg.add_task(run_bg)
    bg.add_task(run_async_bg)


def run_bg():
    with open_session() as session:
        session.execute("SELECT now()").scalar()


async def run_async_bg():
    async with asyncio_support.open_session() as session:
        await session.execute("SELECT now()").scalar()

Pagination

from fastapi import APIRouter, Depends
from fastapi_sqla import Base, Page, Paginate
from pydantic import BaseModel
from sqlalchemy import select

router = APIRouter()


class User(Base):
    __tablename__ = "user"


class UserModel(BaseModel):
    id: int
    name: str


@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: Paginate = Depends()):
    return paginate(select(User))

By default:

• It returns pages of 10 items, up to 100 items;

• Total number of items in the collection is queried using Query.count for legacy orm queries and the equivalent for 2.0 style queries.

• Response example for /users?offset=40&limit=10:

  {
      "data": [
          {
              "id": 41,
              "name": "Pat Thomas"
          },
          {
              "id": 42,
              "name": "Mulatu Astatke"
          }
      ],
      "meta": {
          "offset": 40,
          "total_items": 42,
          "total_pages": 5,
          "page_number": 5
      }
  }
  

Customize pagination

You can customize:

• Minimum and maximum number of items per pages;
• How the total number of items in the collection is queried;

To customize pagination, create a dependency using fastapi_sqla.Pagination

from fastapi import APIRouter, Depends
from fastapi_sqla import Base, Page, Pagination, Session
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.sql import Select

router = APIRouter()


class User(Base):
    __tablename__ = "user"


class UserModel(BaseModel):
    id: int
    name: str


def query_count(session: Session, query: Select) -> int:
    return session.execute(select(func.count()).select_from(User)).scalar()


Paginate = Pagination(min_page_size=5, max_page_size=500, query_count=query_count)


@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: Paginate = Depends()):
    return paginate(select(User))

Pytest fixtures

This library provides a set of utility fixtures, through its PyTest plugin, which is automatically installed with the library.

By default, no records are actually written to the database when running tests. There currently is no way to change this behaviour.

sqla_modules

You must define this fixture, in order for the plugin to reflect table metadata in your SQLAlchemy entities. It should just import all of the application's modules which contain SQLAlchemy models.

Example:

# tests/conftest.py
from pytest import fixture


@fixture
def sqla_modules():
    from er import sqla  # noqa

db_url

The DB url to use.

When CI key is set in environment variables, it defaults to using postgres as the host name:

postgresql://postgres@posgres/postgres

In other cases, the host is set to localhost:

postgresql://postgres@localhost/postgres

Of course, you can override it by overloading the fixture:

from pytest import fixture


@fixture(scope="session")
def db_url():
    return "postgresql://postgres@localhost/test_database"

async_sqlalchemy_url

DB url to use when using asyncio support. Defaults to db_url fixture with postgresql+asyncpg:// scheme.

session & async_session

Sqla sessions to create db fixture:

• All changes done at test setup or during the test are rollbacked at test tear down;
• No record will actually be written in the database;
• Changes in one regular session need to be committed to be available from other regular sessions;
• Changes in one async session need to be committed to be available from other async sessions;
• Changes from regular sessions are not available from async session and vice-versa even when committed;

Example:

from pytest import fixture


@fixture
def patient(session):
    from er.sqla import Patient
    patient = Patient(first_name="Bob", last_name="David")
    session.add(patient)
    session.commit()
    return patient


@fixture
async def doctor(async_session):
    from er.sqla import Doctor
    doctor = Doctor(name="who")
    async_session.add(doctor)
    await async_session.commit()
    return doctor

db_migration

A session scope fixture that runs alembic upgrade at test session setup and alembic downgrade at tear down.

It depends on alembic_ini_path fixture to get the path of alembic.ini file.

To use in a test or test module:

from pytest import mark

pytestmark = mark.usefixtures("db_migration")

To use globally, add to pytest options:

[pytest]
usefixtures =
    db_migration

Or depends on it in top-level conftest.py and mark it as auto-used:

from pytest import fixture


@fixture(scope="session", autouse=True)
def db_migration(db_migration):
    pass

alembic_ini_path

It returns the path of alembic.ini configuration file. By default, it returns ./alembic.ini.