import typing
import dataclasses

@dataclasses.dataclass(kw_only=True)
class User:
    id: int | None = None
    name: str

@dataclasses.dataclass(kw_only=True)
class Forum:
    id: int | None = None
    name: str

@dataclasses.dataclass(kw_only=True)
class Thread:
    id: int | None = None
    name: str
    forum: int

@dataclasses.dataclass(kw_only=True)
class UserForum:
    user_id: int
    forum_id: int

@dataclasses.dataclass(kw_only=True)
class Message:
    user: User
    content: str
    thread: int
    time: int
    id: int | None = None