Поддерживаются следующие аргументы:

* `allow_origins` - Список источников, на которые разрешено выполнять кросс-доменные запросы. Например, `['https://example.org', 'https://www.example.org']`. Можно использовать `['*']`, чтобы разрешить любые источники.

* Validate **complex structures**:
    * Use of hierarchical Pydantic models, Python `typing`’s `List` and `Dict`, etc.
    * And validators allow complex data schemas to be clearly and easily defined, checked and documented as JSON Schema.
    * You can have deeply **nested JSON** objects and have them all validated and annotated.
* **Extensible**:

!!! note
    FastAPI will know that the value of `q` is not required because of the default value `= None`.

    The `Union` in `Union[str, None]` will allow your editor to give you better support and detect errors.

## Additional validation

We are going to enforce that even though `q` is optional, whenever it is provided, **its length doesn't exceed 50 characters**.

    Use the chat only for other general conversations.

### Don't use the chat for questions

Keep in mind that as chats allow more "free conversation", it's easy to ask questions that are too general and more difficult to answer, so, you might not receive answers.

# OAuth2 scopes

You can use OAuth2 scopes directly with **FastAPI**, they are integrated to work seamlessly.

This would allow you to have a more fine-grained permission system, following the OAuth2 standard, integrated into your OpenAPI application (and the API docs).

OAuth2 with scopes is the mechanism used by many big authentication providers, like Facebook, Google, GitHub, Microsoft, Twitter, etc. They use it to provide specific permissions to users and applications.

But recent versions of Pydantic allow providing a custom class that inherits from `pydantic.utils.GetterDict`, to provide the functionality used when using the `orm_mode = True` to retrieve the values for ORM model attributes.

The following arguments are supported:

* `allow_origins` - A list of origins that should be permitted to make cross-origin requests. E.g. `['https://example.org', 'https://www.example.org']`. You can use `['*']` to allow any origin.
* `allow_origin_regex` - A regex string to match against origins that should be permitted to make cross-origin requests. e.g. `'https://.*\.example\.org'`.

They tend to require more complex configurations, a message/job queue manager, like RabbitMQ or Redis, but they allow you to run background tasks in multiple processes, and especially, in multiple servers.

!!! note
    FastAPI will know that the value of `q` is not required because of the default value `= None`.

    The `Union` in `Union[str, None]` is not used by FastAPI, but will allow your editor to give you better support and detect errors.

## Without Pydantic

```Python
connect_args={"check_same_thread": False}
```

...is needed only for `SQLite`. It's not needed for other databases.

!!! info "Technical Details"

    By default SQLite will only allow one thread to communicate with it, assuming that each thread would handle an independent request.

    This is to prevent accidentally sharing the same connection for different things (for different requests).