# database.py looks roughly like this
_request_id_ctx_var: contextvars.ContextVar[str] = contextvars.ContextVar('request_id_ctx')
def get_request_id() -> str:
 return _request_id_ctx_var.get()
 
@contextmanager
def db_context(identifier: str):
 ctx_token = _request_id_ctx_var.set(identifier)
 yield
 _request_id_ctx_var.reset(ctx_token)
class Database:
 def __init__(self, db_url: str, pool_size: int) -> None:
 self.db_url = db_url
 self._engine = create_async_engine(
 self.db_url,
 echo=False,
 pool_size=pool_size,
 )
 self._create_factory()
 def _create_factory(self, bind: Union[Connection, Engine, None] = None) -> None:
 bind = bind or self._engine
 self.async_session_factory = sessionmaker(
 bind=bind,
 class_=_AsyncSession,
 expire_on_commit=False,
 autoflush=False,
 )
 self.AsyncSession = async_scoped_session(self.async_session_factory, scopefunc=get_request_id)
 def create_session(self):
 return self.AsyncSession()
# In application.py I set up middlewares to set the context
@app.middleware('http')
async def remove_db_session(request: Request, call_next):
 response = await call_next(request)
 db = container.db()
 await db.AsyncSession.remove()
 return response
@app.middleware('http')
async def set_db_context(request: Request, call_next):
 request_id = str(uuid.uuid4())
 with db_context(identifier=request_id):
 response = await call_next(request)
 return response
# And in containers.py
class Container(containers.DeclarativeContainer):
 db = providers.Singleton(Database, db_url=config.database.url, pool_size=config.database.pool_size)
 db_session = providers.Callable(db.provided.create_session.call())
 user_repository = providers.Factory(UserRepository, session=db_session)