我写了下面的代码
views.py

room_list = Room.objects.all()
time_slot_list = TimeSlot.objects.none()
for room in room_list:
    time_slots = TimeSlot.objects.filter(room=room)
    for time_slot in time_slots:
        time_slot_list.union(time_slot)
print(time_slot_list)

models.py

class Room(models.Model):
    class Meta:
      ordering = ['number']
    number =  models.PositiveSmallIntegerField(
        validators=[MaxValueValidator(550), MinValueValidator(1)],
        primary_key=True
        )
    CATEGORIES = (
        ('Regular', 'Regular'),
        ('Executive', 'Executive'),
        ('Deluxe', 'Deluxe'),
    )
    category = models.CharField(max_length=9, choices=CATEGORIES, default='Regular')
    CAPACITY = (
        (1, '1'),
        (2, '2'),
        (3, '3'),
        (4, '4'),
    )
    capacity = models.PositiveSmallIntegerField(
        choices=CAPACITY, default=2
        )
    advance = models.PositiveSmallIntegerField(default=10)
    manager = models.ForeignKey(
        settings.AUTH_USER_MODEL, on_delete=models.CASCADE
    )

class TimeSlot(models.Model):
    class Meta:
        ordering = ['available_from']
    room = models.ForeignKey(Room, on_delete=models.CASCADE)
    available_from = models.TimeField()
    available_till = models.TimeField()

当我打印time_slot_list时，我得到的是空的QuerySet，但我希望它包含时隙列表。
有人能告诉我我做错了什么吗？