wrap lifespan decorator in docs and add missing type (#1362)

Co-authored-by: collerek <[email protected]>

docs/fastapi/index.md

@@ -29,7 +29,7 @@ Here you can find a very simple sample application code.
 Define startup and shutdown procedures using FastAPI lifespan and use is in the
 application.
 ```python
-from typing import List, Optional
+from typing import List, Optional, AsyncIterator
 
 import databases
 import sqlalchemy
@@ -41,22 +41,24 @@ from contextlib import asynccontextmanager
 from fastapi import FastAPI
 
 
-@asynccontextmanager
-async def lifespan(_: FastAPI) -> AsyncIterator[None]:
-    if not config.database.is_connected:
-        await config.database.connect()
+def get_lifespan(config):
+    @asynccontextmanager
+    async def lifespan(_: FastAPI) -> AsyncIterator[None]:
+        if not config.database.is_connected:
+            await config.database.connect()
 
-    yield
-
-    if config.database.is_connected:
-        await config.database.disconnect()
+        yield
 
+        if config.database.is_connected:
+            await config.database.disconnect()
+    return lifespan
 
 base_ormar_config = ormar.OrmarConfig(
     metadata=sqlalchemy.MetaData(),
     database=databases.Database("sqlite:///test.db"),
 )
-app = FastAPI(lifespan=lifespan(base_ormar_config))
+
+app = FastAPI(lifespan=get_lifespan(base_ormar_config))
 ```
 
 !!!info