In some cases, you might still have to use Pydantic's version of `dataclasses`. For example, if you have errors with the automatically generated API documentation.

In that case, you can simply swap the standard `dataclasses` with `pydantic.dataclasses`, which is a drop-in replacement:

{* ../../docs_src/dataclasses_/tutorial003_py310.py hl[1,4,7:10,13:16,22:24,27] *}

1. We still import `field` from standard `dataclasses`.

app = FastAPI(
    servers=[
        {"url": "/", "description": "Default, relative server"},
        {
            "url": "http://staging.localhost.tiangolo.com:8000",
            "description": "Staging but actually localhost still",
        },
        {"url": "https://prod.example.com"},
    ]
)


@app.get("/foo")
def foo():
    return {"message": "Hello World"}


client = TestClient(app)


def test_app():

        example: Annotated[
            Optional[Any],
            deprecated(
                "Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, "
                "although still supported. Use examples instead."
            ),
        ] = _Unset,
        openapi_examples: Optional[dict[str, Example]] = None,
        deprecated: Union[deprecated, str, bool, None] = None,

/// tip

If you need GraphQL, I still would recommend you check out <a href="https://strawberry.rocks/" class="external-link" target="_blank">Strawberry</a>, as it's based on type annotations instead of custom classes and types.

///

## Learn More { #learn-more }

// Here you should declare versions which should be shared by the different modules of buildSrc itself
val javaParserVersion = "3.18.0"
// Note: this currently still contains 3/4 logic as we will temporarily have Groovy 3 for the build itself until we move to a Gradle built with Groovy 4
// It can be removed or changed to 4/5 logic (if necessary) at that point.

            """
        ),
    ] = None,
    example: Annotated[
        Optional[Any],
        deprecated(
            "Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, "
            "although still supported. Use examples instead."
        ),
    ] = _Unset,
    openapi_examples: Annotated[
        Optional[dict[str, Example]],
        Doc(
            """
            OpenAPI-specific examples.

common:monolithic --define framework_shared_object=false
common:monolithic --define tsl_protobuf_header_only=false
common:monolithic --experimental_link_static_libraries_once=false  # b/229868128

# Please note that MKL on MacOS is still not supported.
# If you would like to use a local MKL instead of downloading, please set the
# environment variable "TF_MKL_ROOT" every time before build.
common:mkl --define=build_with_mkl=true --define=enable_mkl=true

    example: Annotated[
        Optional[Any],
        typing_deprecated(
            "Deprecated in OpenAPI 3.1.0 that now uses JSON Schema 2020-12, "
            "although still supported. Use examples instead."
        ),
    ] = None


# Ref: https://json-schema.org/draft/2020-12/json-schema-core.html#name-json-schema-documents
# A JSON Schema MUST be an object or a boolean.

### Pydantic v1

**This version of FastAPI still supports Pydantic v1**. And although Pydantic v1 will be deprecated at some point, it will still be supported for a while.