/// info

Keep in mind that dataclasses can't do everything Pydantic models can do.

So, you might still need to use Pydantic models.

But if you have a bunch of dataclasses laying around, this is a nice trick to use them to power a web API using FastAPI. 🤓

///

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

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

    operation_id = f"{operation_id}_{method.lower()}"
    return operation_id


def generate_unique_id(route: "APIRoute") -> str:
    operation_id = f"{route.name}{route.path_format}"
    operation_id = re.sub(r"\W", "_", operation_id)
    assert route.methods
    operation_id = f"{operation_id}_{list(route.methods)[0].lower()}"
    return operation_id

        api("org.jetbrains.dokka:dokka-gradle-plugin:2.0.0")
        api("com.fasterxml.woodstox:woodstox-core:6.4.0") {
            because("CVE-2022-40152 on lower versions")
        }
        api("com.fasterxml.jackson:jackson-bom:2.16.1") {
            because("CVE-2025-52999 on lower versions")
        }
        api("com.beust:jcommander:1.78")
        api("$groovyGroup:groovy:$groovyVersion")

    assert encoded_instance2["dt_field"] == instance["dt_field"].isoformat()


def test_custom_enum_encoders():
    def custom_enum_encoder(v: Enum):
        return v.value.lower()

    class MyEnum(Enum):
        ENUM_VAL_1 = "ENUM_VAL_1"

    instance = MyEnum.ENUM_VAL_1

    encoded_instance = jsonable_encoder(
        instance, custom_encoder={MyEnum: custom_enum_encoder}

            We check the binary compatibility by comparing the current code’s binary interfaces
            against THE LATEST VERSION WHICH IS RELEASED FROM RELEASE BRANCH (from `released-version.json` on this branch)
            AND LOWER THAN CURRENT BASE VERSION (from `version.txt` on this branch).

                        }
                    )
            if route.openapi_extra:
                deep_dict_update(operation, route.openapi_extra)
            path[method.lower()] = operation
    return path, security_schemes, definitions


def get_fields_from_routes(
    routes: Sequence[BaseRoute],
) -> list[ModelField]:
    body_fields_from_routes: list[ModelField] = []

        Item(name="Plumbus", price=32.0),
    ]
```

FastAPI will use the return type annotation to perform:

* Data validation
* Automatic documentation
    * It could power automatic client generators
* **Data filtering**

Before this version it was only supported via the `response_model` parameter.