{
                    "annotation": annotation,
                    "alias_priority": alias_priority,
                    "validation_alias": validation_alias,
                    "serialization_alias": serialization_alias,
                    "strict": strict,
                    "json_schema_extra": current_json_schema_extra,
                }
            )
            kwargs["pattern"] = pattern or regex

    * If you didn't use FastAPI and used Starlette directly (or another tool, like Sanic, Flask, Responder, etc) you would have to implement all the data validation and serialization yourself. So, your final application would still have the same overhead...

            """
        ),
    ] = None,
    serialization_alias: Annotated[
        Union[str, None],
        Doc(
            """
            'Blacklist' validation step. The vanilla parameter field will be the
            single one of the alias' or set of aliases' fields and all the other
            fields will be ignored at serialization time.
            """
        ),
    ] = None,
    title: Annotated[

But as TypeScript data is not preserved after compilation to JavaScript, it cannot rely on the types to define validation, serialization and documentation at the same time. Due to this and some design decisions, to get validation, serialization and automatic schema generation, it's needed to add decorators in many places. So, it becomes quite verbose.

!!! info
    你还可以使用：

    * `response_model_exclude_defaults=True`
    * `response_model_exclude_none=True`

And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

!!! info

!!! info "情報"
    以下も使用することができます:

    * `response_model_exclude_defaults=True`
    * `response_model_exclude_none=True`

    required: Union[bool, UndefinedType] = Undefined,
    model_config: Type[BaseConfig] = BaseConfig,
    field_info: Optional[FieldInfo] = None,
    alias: Optional[str] = None,
    mode: Literal["validation", "serialization"] = "validation",
) -> ModelField:
    """
    Create a new response field. Raises if type_ is invalid.
    """
    class_validators = class_validators or {}
    if PYDANTIC_V2:

!!! info
    You can also use:

    * `response_model_exclude_defaults=True`
    * `response_model_exclude_none=True`

```

In this case, `item_id` is declared to be an `int`.

!!! check
    This will give you editor support inside of your function, with error checks, completion, etc.

## Data <abbr title="also known as: serialization, parsing, marshalling">conversion</abbr>

If you run this example and open your browser at <a href="http://127.0.0.1:8000/items/3" class="external-link" target="_blank">http://127.0.0.1:8000/items/3</a>, you will see a response of: