Body() — fastapi Function Reference

Architecture documentation for the Body() function in param_functions.py from the fastapi codebase.

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Dependency Diagram

graph TD
  fe334cb9_2aa9_5ea2_a997_981d68b98b86["Body()"]
  24a9a43e_697f_81ce_6a7c_28a423a6f93b["param_functions.py"]
  fe334cb9_2aa9_5ea2_a997_981d68b98b86 -->|defined in| 24a9a43e_697f_81ce_6a7c_28a423a6f93b
  style fe334cb9_2aa9_5ea2_a997_981d68b98b86 fill:#6366f1,stroke:#818cf8,color:#fff

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Source Code

fastapi/param_functions.py lines 1324–1651

def Body(  # noqa: N802
    default: Annotated[
        Any,
        Doc(
            """
            Default value if the parameter field is not set.
            """
        ),
    ] = Undefined,
    *,
    default_factory: Annotated[
        Union[Callable[[], Any], None],
        Doc(
            """
            A callable to generate the default value.

            This doesn't affect `Path` parameters as the value is always required.
            The parameter is available only for compatibility.
            """
        ),
    ] = _Unset,
    embed: Annotated[
        Union[bool, None],
        Doc(
            """
            When `embed` is `True`, the parameter will be expected in a JSON body as a
            key instead of being the JSON body itself.

            This happens automatically when more than one `Body` parameter is declared.

            Read more about it in the
            [FastAPI docs for Body - Multiple Parameters](https://fastapi.tiangolo.com/tutorial/body-multiple-params/#embed-a-single-body-parameter).
            """
        ),
    ] = None,
    media_type: Annotated[
        str,
        Doc(
            """
            The media type of this parameter field. Changing it would affect the
            generated OpenAPI, but currently it doesn't affect the parsing of the data.
            """
        ),
    ] = "application/json",
    alias: Annotated[
        Optional[str],
        Doc(
            """
            An alternative name for the parameter field.

            This will be used to extract the data and for the generated OpenAPI.
            It is particularly useful when you can't use the name you want because it
            is a Python reserved keyword or similar.
            """
        ),
    ] = None,
    alias_priority: Annotated[
        Union[int, None],
        Doc(
            """
            Priority of the alias. This affects whether an alias generator is used.
            """
        ),
    ] = _Unset,
    validation_alias: Annotated[
        Union[str, AliasPath, AliasChoices, None],
        Doc(
            """
            'Whitelist' validation step. The parameter field will be the single one
            allowed by the alias or set of aliases defined.
            """
        ),
    ] = 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.
            """