ModelField Class — fastapi Architecture

Source Code

fastapi/_compat/v2.py lines 82–186

class ModelField:
    field_info: FieldInfo
    name: str
    mode: Literal["validation", "serialization"] = "validation"
    config: Union[ConfigDict, None] = None

    @property
    def alias(self) -> str:
        a = self.field_info.alias
        return a if a is not None else self.name

    @property
    def validation_alias(self) -> Union[str, None]:
        va = self.field_info.validation_alias
        if isinstance(va, str) and va:
            return va
        return None

    @property
    def serialization_alias(self) -> Union[str, None]:
        sa = self.field_info.serialization_alias
        return sa or None

    @property
    def default(self) -> Any:
        return self.get_default()

    def __post_init__(self) -> None:
        with warnings.catch_warnings():
            # Pydantic >= 2.12.0 warns about field specific metadata that is unused
            # (e.g. `TypeAdapter(Annotated[int, Field(alias='b')])`). In some cases, we
            # end up building the type adapter from a model field annotation so we
            # need to ignore the warning:
            if shared.PYDANTIC_VERSION_MINOR_TUPLE >= (2, 12):
                from pydantic.warnings import UnsupportedFieldAttributeWarning

                warnings.simplefilter(
                    "ignore", category=UnsupportedFieldAttributeWarning
                )
            # TODO: remove after setting the min Pydantic to v2.12.3
            # that adds asdict(), and use self.field_info.asdict() instead
            field_dict = asdict(self.field_info)
            annotated_args = (
                field_dict["annotation"],
                *field_dict["metadata"],
                # this FieldInfo needs to be created again so that it doesn't include
                # the old field info metadata and only the rest of the attributes
                Field(**field_dict["attributes"]),
            )
            self._type_adapter: TypeAdapter[Any] = TypeAdapter(
                Annotated[annotated_args],
                config=self.config,
            )

    def get_default(self) -> Any:
        if self.field_info.is_required():
            return Undefined
        return self.field_info.get_default(call_default_factory=True)

    def validate(
        self,
        value: Any,
        values: dict[str, Any] = {},  # noqa: B006
        *,
        loc: tuple[Union[int, str], ...] = (),
    ) -> tuple[Any, list[dict[str, Any]]]:
        try:
            return (
                self._type_adapter.validate_python(value, from_attributes=True),
                [],
            )
        except ValidationError as exc:
            return None, _regenerate_error_with_loc(
                errors=exc.errors(include_url=False), loc_prefix=loc
            )

    def serialize(
        self,
        value: Any,
        *,
        mode: Literal["json", "python"] = "json",