use the proper 'async_sessionmaker' factory

Signed-off-by: Grant Ramsay <seapagan@gmail.com>

Author: seapagan

db.py

@@ -1,12 +1,9 @@
-from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
-from sqlalchemy.orm import declarative_base, sessionmaker
+"""Set up the database connection and session.""" ""
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.orm import declarative_base
 
 DATABASE_URL = "postgresql+asyncpg://postgres:postgres@localhost/postgres"
 
 engine = create_async_engine(DATABASE_URL, echo=False)
 Base = declarative_base()
-
-
-async_session = sessionmaker(
-    engine, class_=AsyncSession, expire_on_commit=False  # type: ignore
-)
+async_session = async_sessionmaker(engine, expire_on_commit=False)

main.py

@@ -1,3 +1,4 @@
+"""An example of using FastAPI with Async SQLAlchemy 2."""
 import subprocess
 from contextlib import asynccontextmanager
 
@@ -29,8 +30,11 @@ async def lifespan(app: FastAPI):
 
 
 async def get_db():
-    """Get a database session."""
-    async with async_session() as session:  # type: ignore
+    """Get a database session.
+
+    To be used for dependency injection.
+    """
+    async with async_session() as session:
         async with session.begin():
             yield session