[Issue #1312]: full examples use lifespan instead of on_startup (#1363)

* docs(examples): full examples use lifespan instead of on_startup for database initialization

* Update beanie.md

Replaced the annotations on the notes that I missed

examples/sqlalchemy/app/app.py

@@ -1,10 +1,20 @@
+from contextlib import asynccontextmanager
+
 from fastapi import Depends, FastAPI
 
 from app.db import User, create_db_and_tables
 from app.schemas import UserCreate, UserRead, UserUpdate
 from app.users import auth_backend, current_active_user, fastapi_users
 
-app = FastAPI()
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # Not needed if you setup a migration system like Alembic
+    await create_db_and_tables()
+    yield
+
+
+app = FastAPI(lifespan=lifespan)
 
 app.include_router(
     fastapi_users.get_auth_router(auth_backend), prefix="/auth/jwt", tags=["auth"]
@@ -34,9 +44,3 @@ app.include_router(
 @app.get("/authenticated-route")
 async def authenticated_route(user: User = Depends(current_active_user)):
     return {"message": f"Hello {user.email}!"}
-
-
-@app.on_event("startup")
-async def on_startup():
-    # Not needed if you setup a migration system like Alembic
-    await create_db_and_tables()