如何扩展 Pydantic 对象并更改某些字段的类型？

有两个类似的 pydantic 对象。唯一的区别是有些字段是可选的。 如何只定义一个对象中的字段并扩展到另一个对象中？

class ProjectCreateObject(BaseModel):
    project_id: str
    project_name: str
    project_type: ProjectTypeEnum
    depot: str
    system: str
    ...

class ProjectPatchObject(ProjectCreateObject):
    project_id: str
    project_name: Optional[str]
    project_type: Optional[ProjectTypeEnum]
    depot: Optional[str]
    system: Optional[str]
    ...

我找到了一个好又简单的方法__init__subclass__。 文档也可以成功生成。

class ProjectCreateObject(BaseModel):
    project_id: str
    project_name: str
    project_type: ProjectTypeEnum
    depot: str
    system: str
    ...

    def __init_subclass__(cls, optional_fields=(), **kwargs):
        """
        allow some fields of subclass turn into optional
        """
        super().__init_subclass__(**kwargs)
        for field in optional_fields:
            cls.__fields__[field].outer_type_ = Optional
            cls.__fields__[field].required = False

_patch_fields = ProjectCreateObject.__fields__.keys() - {'project_id'}

class ProjectPatchObject(ProjectCreateObject, optional_fields=_patch_fields):
    pass