parse_dont_validate.py

@dataclass
class FieldUpdate
    field_name: str
    value: Any  # ``Any`` and ``Union`` are taken from the ``typing`` module.
    invalid_reason: Union[FieldErrors.Unknown, FieldErrors.Immutable, None]

class ModelUpdate:
    def __init__(self, model_class, request_body):
        updates = []

        for field, value in request_body.items():
            ...  # We'd check whether the field is known and mutable here.
            updates.append(FieldUpdate(field, value, field_error))

        self.updates = updates

    def apply(self, model_obj):
        if any(u.invalid_reason for u in self.updates):
            raise InvalidUpdateError(...)

        for update in self.updates:
            setattr(model_obj, update.field, update.value)