Fastapi-SQLA is an SQLAlchemy extension for FastAPI easy to setup with support for pagination, asyncio, SQLModel and pytest. It supports SQLAlchemy>=1.3 and is fully compliant with SQLAlchemy 2.0. It is developped, maintained and used on production by the team at @dialoguemd with love from Montreal 🇨🇦.
Using pip:
pip install fastapi-sqla
Note that you need a SQLAlchemy compatible engine adapter. We test with psycopg2 which you can install using the psycopg2 extra.
Assuming it runs against a DB with a table user with 3 columns, id, name and
unique email:
# main.py
from contextlib import asynccontextmanager
from fastapi import FastAPI, HTTPException
from fastapi_sqla import Base, Item, Page, Paginate, Session, setup_middlewares, startup
from pydantic import BaseModel, EmailStr
from sqlalchemy import select
from sqlalchemy.exc import IntegrityError
@asynccontextmanager
async def lifespan(app: FastAPI):
await startup()
yield
app = FastAPI(lifespan=lifespan)
setup_middlewares(app)
class User(Base):
__tablename__ = "user"
class UserIn(BaseModel):
name: str
email: EmailStr
class UserModel(UserIn):
id: int
class Config:
orm_mode = True
@app.get("/users", response_model=Page[UserModel])
def list_users(paginate: Paginate):
return paginate(select(User))
@app.get("/users/{user_id}", response_model=Item[UserModel])
def get_user(user_id: int, session: Session):
user = session.get(User, user_id)
if user is None:
raise HTTPException(404)
return {"data": user}
@app.post("/users", response_model=Item[UserModel])
def create_user(new_user: UserIn, session: Session):
user = User(**new_user.model_dump())
session.add(user)
try:
session.flush()
except IntegrityError:
raise HTTPException(409, "Email is already taken.")
return {"data": user}Creating a db using sqlite3:
sqlite3 db.sqlite <<EOF
CREATE TABLE user (
id INTEGER PRIMARY KEY AUTOINCREMENT,
email TEXT NOT NULL,
name TEXT NOT NULL
);
CREATE UNIQUE INDEX user_email_idx ON user (email);
EOFRunning the app:
sqlalchemy_url=sqlite:///db.sqlite?check_same_thread=false uvicorn main:appThe 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, example:
export sqlalchemy_url=postgresql://postgres@localhostIn order to configure multiple sessions for the application,
set the environment variables with this prefix format: fastapi_sqla__MY_KEY__.
As with the default session, each matching key (after the prefix is stripped)
is treated as though it were the corresponding keyword argument to sqlalchemy.create_engine
call.
For example, to configure a session with the read_only key:
export fastapi_sqla__read_only__sqlalchemy_url=postgresql://postgres@localhostasyncio support using asyncpg
SQLAlchemy >= 1.4 supports asyncio.
To enable asyncio support against a Postgres DB, install asyncpg:
pip install asyncpgAnd define the environment variable sqlalchemy_url with postgres+asyncpg scheme:
export sqlalchemy_url=postgresql+asyncpg://postgres@localhostimport fastapi_sqla
from fastapi import FastAPI
@asynccontextmanager
async def lifespan(app: FastAPI):
await fastapi_sqla.startup()
yield
app = FastAPI(lifespan=lifespan)
fastapi_sqla.setup_middlewares(app)import fastapi_sqla
from fastapi import FastAPI
app = FastAPI()
fastapi_sqla.setup(app)from fastapi_sqla import Base
class Entity(Base):
__tablename__ = "table-name-in-db"Use FastAPI dependency injection to get a session as a parameter of a path operation function.
The SQLAlchemy session is committed before the response is returned or rollbacked if any exception occurred:
from fastapi import APIRouter
from fastapi_sqla import AsyncSession, Session
router = APIRouter()
@router.get("/example")
def example(session: Session):
return session.execute("SELECT now()").scalar()
@router.get("/async_example")
async def async_example(session: AsyncSession):
return await session.scalar("SELECT now()")In order to get a session configured with a custom key:
from typing import Annotated
from fastapi import APIRouter, Depends
from fastapi_sqla import (
AsyncSessionDependency,
SessionDependency,
SqlaAsyncSession,
SqlaSession,
)
router = APIRouter()
# Preferred
ReadOnlySession = Annotated[SqlaSession, Depends(SessionDependency(key="read_only"))]
AsyncReadOnlySession = Annotated[
SqlaAsyncSession, Depends(AsyncSessionDependency(key="read_only"))
]
@router.get("/example")
def example(session: ReadOnlySession):
return session.execute("SELECT now()").scalar()
@router.get("/async_example")
async def async_example(session: AsyncReadOnlySession):
return await session.scalar("SELECT now()")
# Alternative
@router.get("/example/alt")
def example_alt(session: SqlaSession = Depends(SessionDependency(key="read_only"))):
return session.execute("SELECT now()").scalar()
@router.get("/async_example/alt")
async def async_example_alt(
session: SqlaAsyncSession = Depends(AsyncSessionDependency(key="read_only")),
):
return await session.scalar("SELECT now()")When needing a session outside of a path operation, like when using
FastAPI background tasks, use fastapi_sqla.open_session context manager.
The SQLAlchemy session is committed when exiting context or rollbacked if any exception
occurred:
from fastapi import APIRouter, BackgroundTasks
from fastapi_sqla import open_async_session, open_session
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()
def run_bg_with_key():
with open_session(key="read_only") as session:
session.execute("SELECT now()").scalar()
async def run_async_bg():
async with open_async_session() as session:
await session.scalar("SELECT now()")
async def run_async_bg_with_key():
async with open_async_session(key="read_only") as session:
await session.scalar("SELECT now()")from fastapi import APIRouter
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
class Config:
orm_mode = True
@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: Paginate):
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. -
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 } }
To paginate a query which doesn't return scalars, specify scalars=False when invoking
paginate:
from fastapi import APIRouter
from fastapi_sqla import Base, Page, Paginate
from pydantic import BaseModel
from sqlalchemy import func, select
from sqlalchemy.orm import relationship
router = APIRouter()
class User(Base):
__tablename__ = "user"
notes = relationship("Note")
class Note(Base):
__tablename__ = "note"
class UserModel(BaseModel):
id: int
name: str
notes_count: int
@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: Paginate):
query = (
select(User.id, User.name, func.count(Note.id).label("notes_count"))
.join(Note)
.group_by(User)
)
return paginate(query, scalars=False)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
router = APIRouter()
class User(Base):
__tablename__ = "user"
class UserModel(BaseModel):
id: int
name: str
def query_count(session: Session) -> int:
return session.execute(select(func.count()).select_from(User)).scalar()
CustomPaginate = Pagination(min_page_size=5, max_page_size=500, query_count=query_count)
@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: CustomPaginate = Depends()):
return paginate(select(User))When using the asyncio support, use the AsyncPaginate dependency:
from fastapi import APIRouter
from fastapi_sqla import Base, Page, AsyncPaginate
from pydantic import BaseModel
from sqlalchemy import select
router = APIRouter()
class User(Base):
__tablename__ = "user"
class UserModel(BaseModel):
id: int
name: str
class Config:
orm_mode = True
@router.get("/users", response_model=Page[UserModel])
async def all_users(paginate: AsyncPaginate):
return await paginate(select(User))Customize pagination by creating a dependency using fastapi_sqla.AsyncPagination:
from fastapi import APIRouter, Depends
from fastapi_sqla import Base, Page, AsyncPagination, AsyncSession
from pydantic import BaseModel
from sqlalchemy import func, select
router = APIRouter()
class User(Base):
__tablename__ = "user"
class UserModel(BaseModel):
id: int
name: str
async def query_count(session: AsyncSession) -> int:
result = await session.execute(select(func.count()).select_from(User))
return result.scalar()
CustomPaginate = AsyncPagination(min_page_size=5, max_page_size=500, query_count=query_count)
@router.get("/users", response_model=Page[UserModel])
async def all_users(paginate: CustomPaginate = Depends()):
return await paginate(select(User))Pagination supports multiple sessions as well. To paginate using a session configured with a custom key:
from typing import Annotated
from fastapi import APIRouter, Depends
from fastapi_sqla import (
AsyncPaginateSignature,
AsyncPagination,
Base,
Page,
PaginateSignature,
Pagination,
)
from pydantic import BaseModel
from sqlalchemy import func, select
router = APIRouter()
class User(Base):
__tablename__ = "user"
class UserModel(BaseModel):
id: int
name: str
# Preferred
ReadOnlyPaginate = Annotated[
PaginateSignature, Depends(Pagination(session_key="read_only"))
]
AsyncReadOnlyPaginate = Annotated[
AsyncPaginateSignature, Depends(AsyncPagination(session_key="read_only"))
]
@router.get("/users", response_model=Page[UserModel])
def all_users(paginate: ReadOnlyPaginate):
return paginate(select(User))
@router.get("/async_users", response_model=Page[UserModel])
async def async_all_users(paginate: AsyncReadOnlyPaginate):
return await paginate(select(User))
# Alternative
@router.get("/users/alt", response_model=Page[UserModel])
def all_users_alt(
paginate: PaginateSignature = Depends(
Pagination(session_key="read_only")
),
):
return paginate(select(User))
@router.get("/async_users/alt", response_model=Page[UserModel])
async def async_all_users_alt(
paginate: AsyncPaginateSignature = Depends(
AsyncPagination(session_key="read_only")
),
):
return await paginate(select(User))If your project uses SQLModel, then Session dependency is an SQLModel session::
from http import HTTPStatus
from fastapi import FastAPI, HTTPException
from fastapi_sqla import Item, Page, Paginate, Session, setup
from sqlmodel import Field, SQLModel, select
class Hero(SQLModel, table=True):
id: int | None = Field(default=None, primary_key=True)
name: str
secret_name: str
age: int | None = None
app = FastAPI()
setup(app)
@app.get("/heros", response_model=Page[Hero])
def list_hero(paginate: Paginate) -> Page[Hero]:
return paginate(select(Hero))
@app.get("/heros/{hero_id}", response_model=Item[Hero])
def get_hero(hero_id: int, session: Session) -> Item[Hero]:
hero = session.get(Hero, hero_id)
if hero is None:
raise HTTPException(HTTPStatus.NOT_FOUND)
return {"data": hero}This library provides a set of utility fixtures, through its PyTest plugin, which is
automatically installed with the library. Using the plugin requires the pytest_plugin extra.
By default, no records are actually written to the database when running tests. There currently is no way to change this behaviour.
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 app import sqla # noqaThe DB url to use.
When CI key is set in environment variables, it defaults to using postgres as the
host name:
postgresql://postgres@postgres/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"DB url to use when using asyncio support. Defaults to db_url fixture with
postgresql+asyncpg:// scheme.
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
asyncsession 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 doctorA 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_migrationOr 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):
passIt returns the path of alembic.ini configuration file. By default, it returns
./alembic.ini.
- Python >=3.9
- Poetry to install package dependencies.
- A postgres DB reachable at
postgresql://postgres@localhost/postgres
$ poetry install --all-extras$ poetry run pytest$ poetry run tox
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