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SQLAlchemy

FastAPI Users provides the necessary tools to work with SQL databases thanks to SQLAlchemy ORM with asyncio.

Warning

The previous adapter using encode/databases is now deprecated but can still be installed using fastapi-users[sqlalchemy].

Asynchronous driver

To work with your DBMS, you'll need to install the corresponding asyncio driver. The common choices are:

  • For PostgreSQL: pip install asyncpg
  • For SQLite: pip install aiosqlite

For the sake of this tutorial from now on, we'll use a simple SQLite databse.

Setup User table

Let's declare our SQLAlchemy User table.

from typing import AsyncGenerator

from fastapi import Depends
from fastapi_users.db import SQLAlchemyBaseUserTable, SQLAlchemyUserDatabase
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.ext.declarative import DeclarativeMeta, declarative_base
from sqlalchemy.orm import sessionmaker

from .models import UserDB

DATABASE_URL = "sqlite+aiosqlite:///./test.db"
Base: DeclarativeMeta = declarative_base()


class UserTable(Base, SQLAlchemyBaseUserTable):
    pass


engine = create_async_engine(DATABASE_URL)
async_session_maker = sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


async def create_db_and_tables():
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)


async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    async with async_session_maker() as session:
        yield session


async def get_user_db(session: AsyncSession = Depends(get_async_session)):
    yield SQLAlchemyUserDatabase(UserDB, session, UserTable)

As you can see, FastAPI Users provides a mixin that will include base fields for our User table. You can of course add you own fields there to fit to your needs!

Implement a function to create the tables

We'll now create an utility function to create all the defined tables.

from typing import AsyncGenerator

from fastapi import Depends
from fastapi_users.db import SQLAlchemyBaseUserTable, SQLAlchemyUserDatabase
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.ext.declarative import DeclarativeMeta, declarative_base
from sqlalchemy.orm import sessionmaker

from .models import UserDB

DATABASE_URL = "sqlite+aiosqlite:///./test.db"
Base: DeclarativeMeta = declarative_base()


class UserTable(Base, SQLAlchemyBaseUserTable):
    pass


engine = create_async_engine(DATABASE_URL)
async_session_maker = sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


async def create_db_and_tables():
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)


async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    async with async_session_maker() as session:
        yield session


async def get_user_db(session: AsyncSession = Depends(get_async_session)):
    yield SQLAlchemyUserDatabase(UserDB, session, UserTable)

This function can be called, for example, during the initialization of your FastAPI app.

Warning

In production, it's strongly recommended to setup a migration system to update your SQL schemas. See Alembic.

Create the database adapter dependency

The database adapter of FastAPI Users makes the link between your database configuration and the users logic. It should be generated by a FastAPI dependency.

from typing import AsyncGenerator

from fastapi import Depends
from fastapi_users.db import SQLAlchemyBaseUserTable, SQLAlchemyUserDatabase
from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
from sqlalchemy.ext.declarative import DeclarativeMeta, declarative_base
from sqlalchemy.orm import sessionmaker

from .models import UserDB

DATABASE_URL = "sqlite+aiosqlite:///./test.db"
Base: DeclarativeMeta = declarative_base()


class UserTable(Base, SQLAlchemyBaseUserTable):
    pass


engine = create_async_engine(DATABASE_URL)
async_session_maker = sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


async def create_db_and_tables():
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)


async def get_async_session() -> AsyncGenerator[AsyncSession, None]:
    async with async_session_maker() as session:
        yield session


async def get_user_db(session: AsyncSession = Depends(get_async_session)):
    yield SQLAlchemyUserDatabase(UserDB, session, UserTable)

Notice that we define first a get_async_session dependency returning us a fresh SQLAlchemy session to interact with the database.

It's then used inside the get_user_db dependency to generate our adapter. Notice that we pass it three things:

  • A reference to your UserDB model.
  • The session instance we just injected.
  • The UserTable variable, which is the actual SQLAlchemy model.
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