# Dependencies with yield

FastAPI supports dependencies that do some <abbr title='sometimes also called "exit code", "cleanup code", "teardown code", "closing code", "context manager exit code", etc.'>extra steps after finishing</abbr>.

To do this, use `yield` instead of `return`, and write the extra steps (code) after.

!!! tip
    Make sure to use `yield` one single time.

!!! note "Technical Details"
    Any function that is valid to use with:

            background_tasks=background_tasks,
            response=response,
            dependency_overrides_provider=dependency_overrides_provider,
            dependency_cache=dependency_cache,
            async_exit_stack=async_exit_stack,
        )
        (
            sub_values,
            sub_errors,
            background_tasks,
            _,  # the subdependency returns the same response we have

    This way we make sure the database session is always closed after the request. Even if there was an exception while processing the request.

    But you can't raise another exception from the exit code (after `yield`). See more in [Dependencies with `yield` and `HTTPException`](dependencies/dependencies-with-yield.md#dependencies-with-yield-and-httpexception){.internal-link target=_blank}

    except Exception as e:
        ok = bool(
            await anyio.to_thread.run_sync(
                cm.__exit__, type(e), e, None, limiter=exit_limiter
            )
        )
        if not ok:
            raise e
    else:
        await anyio.to_thread.run_sync(
            cm.__exit__, None, None, None, limiter=exit_limiter

# Abhängigkeiten mit yield

FastAPI unterstützt Abhängigkeiten, die nach Abschluss einige <abbr title="Manchmal auch genannt „Exit Code“, „Cleanup Code“, „Teardown Code“, „Closing Code“, „Kontext Manager Exit Code“, usw.">zusätzliche Schritte ausführen</abbr>.

Verwenden Sie dazu `yield` statt `return` und schreiben Sie die zusätzlichen Schritte / den zusätzlichen Code danach.

!!! tip "Tipp"
    Stellen Sie sicher, dass Sie `yield` nur einmal pro Abhängigkeit verwenden.

class MySuperContextManager:
    def __init__(self):
        self.db = DBSession()

    def __enter__(self):
        return self.db

    def __exit__(self, exc_type, exc_value, traceback):
        self.db.close()


async def get_db():
    with MySuperContextManager() as db:

        logging.error(f"Error parsing event file: {e.errors()}")
        sys.exit(0)
    use_pr: Union[PullRequest, None] = None
    for pr in repo.get_pulls():
        if pr.head.sha == event.workflow_run.head_commit.id:
            use_pr = pr
            break
    if not use_pr:
        logging.error(f"No PR found for hash: {event.workflow_run.head_commit.id}")
        sys.exit(0)
    github_headers = {

# Зависимости с yield

FastAPI поддерживает зависимости, которые выполняют некоторые <abbr title='также известные как "exit", "cleanup", "teardown", "close", "context managers", ...'>дополнительные действия после завершения работы</abbr>.

Для этого используйте `yield` вместо `return`, а дополнительный код напишите после него.

!!! tip "Подсказка"
    Обязательно используйте `yield` один-единственный раз.

!!! note "Технические детали"

# 使用yield的依赖项

FastAPI支持在完成后执行一些<abbr title='有时也被称为“退出”("exit")，“清理”("cleanup")，“拆卸”("teardown")，“关闭”("close")，“上下文管理器”("context managers")。 ...'>额外步骤</abbr>的依赖项.

为此，请使用 `yield` 而不是 `return`，然后再编写额外的步骤（代码）。

!!! tip "提示"
    确保只使用一次 `yield` 。

!!! note "技术细节"

    任何一个可以与以下内容一起使用的函数：

    * <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a> 或者

            async with AsyncExitStack() as async_exit_stack:
                solved_result = await solve_dependencies(
                    request=request,
                    dependant=dependant,
                    body=body,
                    dependency_overrides_provider=dependency_overrides_provider,
                    async_exit_stack=async_exit_stack,
                )