from typing import ClassVar, Optional


class ModelItem:
    main_key: ClassVar[str] = ""

    def __init_subclass__(cls) -> None:
        if not cls.main_key:
            raise ValueError("Must specify main_key str class attribute.")

        super().__init_subclass__()


    def __new__(cls, *_args, **_kwargs) -> "ModelItem":
        from .model import Model
        cls.parent_model: Optional[Model] = None
        return super().__new__(cls)


    def __setattr__(self, name: str, value) -> None:
        super().__setattr__(name, value)

        if name != "parent_model" and self.parent_model is not None:
            with self.parent_model._sync_lock:
                self.parent_model._changed = True

    def __delattr__(self, name: str) -> None:
        raise NotImplementedError()