Question

测试模型

class Room(models.Model):
    """
    This stores details of rooms available
    """
    name = models.CharField(
        null=False,
        blank=False,
        max_length=100,
        help_text='Enter the name of the room'
    )
    capacity = models.PositiveIntegerField(
        null=False,
        blank=False,
        help_text='Enter the number of person\'s the room can accommodate'
    )
    created_at = models.DateTimeField(auto_now_add=True)
    modified_at = models.DateTimeField(auto_now=True)

我想更新模型，如果它存在且其modified_at时间小于说x时间，否则只需创建模型。在这里参考它是我希望django执行的原始sql。

INSERT INTO room VALUES (1,'2018-04-30 18:15:32.96468+04:30','2018-04-30 18:15:32.96468+04:30','Room-A',30) ON CONFLICT(id) DO UPDATE SET capacity=10 WHERE room.modified_at < '2017-04-30 18:15:32.96468+04:30';

此外，我想知道我写的SQL查询是否是原子的

Answer 1

以下示例可能正常运行

第一个选项

try:
    obj = Room.objects.get(
        id=id, # test with other fields if you want
    )
    if obj.modified_at < DATETIME:
        obj.capacity = 10
        obj.save()
    else:
        obj = Room.objects.create(
            # fields attributes
        )
except Room.DoesNotExist:
    obj = Room.objects.create(
        # fields attributes
    )

第二个选项

或者您可以使用django的Conditional Expression

from django.db.models import F, Case, When
import datetime

your_date = datetime.datetime.now()
condition = Case(When(modified_at__lt=your_date,then=10),default=F('capacity'))

我们会检查modified_at是否小于your_date
那么这个条件的值是10，
否则，我们会使用F('capacity')

其余代码

Room.objects.update_or_create(name='new_name',
           defaults={'name':'new_name','capacity':conditition})

带有django的条件update_or_create

1 个答案: