Metaclass that makes all fields of a Pydantic model optional.

all_optional_metaclass.py

from typing import Any, Dict, Optional, Tuple, Type

import pydantic.main


class AllOptionalMetaclass(pydantic.main.ModelMetaclass):
    """
    Metaclass that makes all fields of a Pydantic model optional.

    This metaclass modifies the class's annotations to make all fields
    optional by wrapping them with the `Optional` type.

    Usage:
        class MyModel(BaseModel, metaclass=AllOptionalMetaclass):
            field1: str
            field2: int
            ...

    The fields defined in the model will be automatically converted to optional
    fields, allowing instances of the model to be created even if not all fields
    are provided during initialization.
    """

    def __new__(
        cls: Type["AllOptionalMetaclass"],
        name: str,
        bases: Tuple[Type[Any], ...],
        namespaces: Dict[str, Any],
        **kwargs: Dict[str, Any],
    ) -> Any:
        annotations = namespaces.get("__annotations__", {})
        for base in bases:
            for ancestor in base.__mro__:
                annotations.update(getattr(ancestor, "__annotations__", {}))
        for field, field_type in annotations.items():
            if not field.startswith("__"):
                # Optional fields are correctly handled
                annotations[field] = Optional[annotations[field]]
        namespaces["__annotations__"] = annotations
        return super().__new__(cls, name, bases, namespaces)