How to pass ORM object in field_validator?

Question

posts = Post.objects.all().alive() is passed via the system to be parsed with List[PostSchema]. How can I achieve the access of ORM passed object, as mentioned below?

# Schema  is slightly extended version of BaseModel
class PostSchema(Schema, ):
    id: int
    created_at: datetime
    updated_at: datetime
    soft_deleted_at: datetime | None = None
    id: int
    title: str
    slug: str
    body: str
    tags: list[TagsSchema]

    comments: SimpleCommentSchema

    @field_validator("comments", mode="before")
    def get_comments(cls, v, info, obj):  # obj is the each-object passed via List[PostSchema]
        comments = PolymorphicComments.objects.filter(
            parent_id=obj.id,
            parent_type=ContentType.objects.get_for_model(obj)).alive()
        return {
            'comment_count': comments.count(),
            'last_comment': comments.last() if comments.exists() else None,
        }
        return {
            'comment_count': 0,
            'last_comment': None
        }

The post object by ORM does not have a comments attribute, it must be a later calculated filled.