## Необязательные параметры { #optional-parameters }

Аналогично, вы можете объявлять необязательные query-параметры, установив их значение по умолчанию, равное `None`:

{* ../../docs_src/query_params/tutorial002_py310.py hl[7] *}

В этом случае, параметр  `q` будет не обязательным и будет иметь значение `None` по умолчанию.

/// check | Важно

import importlib

import pytest
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=needs_py310),
        pytest.param("tutorial002_an_py39"),
        pytest.param("tutorial002_an_py310", marks=needs_py310),
    ],
)
def get_client(request: pytest.FixtureRequest):

from fastapi.testclient import TestClient
from inline_snapshot import snapshot

from tests.utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=[needs_py310]),
        pytest.param("tutorial002_an_py39"),
        pytest.param("tutorial002_an_py310", marks=[needs_py310]),
    ],
)
def get_client(request: pytest.FixtureRequest):

import importlib

import pytest
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=needs_py310),
    ],
)
def get_client(request: pytest.FixtureRequest):
    mod = importlib.import_module(f"docs_src.query_params.{request.param}")

    client = TestClient(mod.app)

import importlib

import pytest
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=needs_py310),
    ],
)
def get_client(request: pytest.FixtureRequest):
    mod = importlib.import_module(f"docs_src.body_updates.{request.param}")

    client = TestClient(mod.app)

from fastapi.testclient import TestClient
from inline_snapshot import snapshot

from tests.utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=[needs_py310]),
        pytest.param("tutorial002_an_py39"),
        pytest.param("tutorial002_an_py310", marks=[needs_py310]),
    ],
)
def get_client(request: pytest.FixtureRequest):

///

## Datenklassen in `response_model` { #dataclasses-in-response-model }

Sie können `dataclasses` auch im Parameter `response_model` verwenden:

{* ../../docs_src/dataclasses_/tutorial002_py310.py hl[1,6:12,18] *}

Die Datenklasse wird automatisch in eine Pydantic-Datenklasse konvertiert.

Auf diese Weise wird deren Schema in der Benutzeroberfläche der API-Dokumentation angezeigt:

///

## Dataclasses in `response_model` { #dataclasses-in-response-model }

You can also use `dataclasses` in the `response_model` parameter:

{* ../../docs_src/dataclasses_/tutorial002_py310.py hl[1,6:12,18] *}

The dataclass will be automatically converted to a Pydantic dataclass.

This way, its schema will show up in the API docs user interface:

<img src="/img/tutorial/dataclasses/image01.png">

import importlib

import pytest
from fastapi.testclient import TestClient

from ...utils import needs_py310


@pytest.fixture(
    name="client",
    params=[
        pytest.param("tutorial002_py39"),
        pytest.param("tutorial002_py310", marks=needs_py310),
    ],
)
def get_client(request: pytest.FixtureRequest):
    mod = importlib.import_module(f"docs_src.response_model.{request.param}")

    client = TestClient(mod.app)

Предположим, у вас есть Pydantic‑модель со значениями по умолчанию, как здесь:

{* ../../docs_src/separate_openapi_schemas/tutorial001_py310.py ln[1:7] hl[7] *}

### Модель для входа { #model-for-input }

Если использовать эту модель как входную, как здесь:

{* ../../docs_src/separate_openapi_schemas/tutorial001_py310.py ln[1:15] hl[14] *}

…то поле `description` **не будет обязательным**, потому что у него значение по умолчанию `None`.