# 지금까지 작성한 코드 생략
class Booking(SQLModel, table=True):
    __tablename__ = "bookings"

    id: int = Field(default=None, primary_key=True)
    when: date
    topic: str
    description: str = Field(sa_type=Text, description="예약 설명")

    time_slot_id: int = Field(foreign_key="time_slots.id")
    time_slot: TimeSlot = Relationship(back_populates="bookings")

    guest_id: int = Field(foreign_key="users.id")
    guest: "User" = Relationship(back_populates="bookings")

    created_at: AwareDatetime = Field(
        default=None,
        nullable=False,
        sa_type=UtcDateTime,
        sa_column_kwargs={
            "server_default": func.now(),
        },
    )
    updated_at: AwareDatetime = Field(
        default=None,
        nullable=False,
        sa_type=UtcDateTime,
        sa_column_kwargs={
            "server_default": func.now(),
            "onupdate": lambda: datetime.now(timezone.utc),
        },
    )