代码之家 › 专栏 › 技术社区 › Dave

在Django中,我如何构建查询集,以便在时间片上按时间进行过滤?

django-filter django-queryset datetime django python-3.x

1

Dave · 技术社区 · 4 年前

我使用的是Python 3.9和Django 3.2。我有这个价格模型

class Price(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    price = models.FloatField(null=False)
    created = models.DateTimeField(null=False, default=datetime.now)

如果我想得到过去24小时内每小时的价格,我可以运行这样的方法

def _get_prices_per_time_slice(self, last_hours=24):
    now = timezone.now()
    end_time = now.replace(second = 0, microsecond = 0)
    start_time = end_time - timedelta(hours=last_hours)
    qset = Price.objects.filter(
        created__range=[start_time, end_time],
        created__minute=end_time.minute
    ).values('price')
    return [r['price'] for r in qset]

但假设我想每X个小时得到一次价格。

def _get_prices_per_time_slice(self, last_hours=24, time_slice_in_hours=4):

因此,如果当前时间是午夜(零秒零分),我想获得午夜、晚上8点、下午4点、中午、上午8点和凌晨4点的价格。如何添加过滤器以每X小时筛选一次价格?

0 回复 | 直到 4 年前

1

-1

Archana David 4 年前

python中的range函数有助于指定增量步长值

语法: range(start, stop, step)


x = range(3, 20, 4)

for n in x:
  print(n)
#Gives output 
>>> 3
>>> 7
>>> 11
>>> 15
>>> 19

只需重写 created_range 添加步长值 time_slice_in_hours

   created__range=[start_time, end_time, time_slice_in_hours]

选项1


def _get_prices_per_time_slice(self, last_hours= 24,time_slice_in_hours=4):
    now = timezone.now()
    end_time = now.replace(second = 0, microsecond = 0)
    start_time = end_time - timedelta(hours=last_hours)
    qset = Price.objects.filter(
        created__range=[start_time, end_time, time_slice_in_hours],
        created__minute=end_time.minute
    ).values('price')
    return [r['price'] for r in qset]

但是中的语法 django query set api official documentation 未能在中提及步骤参数 __range() 函数,即它可能不受支持 created__range .

选项2

在这种情况下,您可以使用以下函数来计算时间范围 x_time_slice_list 使用Python DateTimeRange 作用 official documentation )并评估为 created__in


from datetimerange import DateTimeRange
from dateutil.relativedelta import relativedelta

def _get_prices_per_time_slice(self, last_hours= 24,time_slice_in_hours=4):
    now = timezone.now()
    end_time = now.replace(second = 0, microsecond = 0)
    start_time = end_time - timedelta(hours=last_hours)
    x_time_slice_list= []

    time_range = DateTimeRange(start_time, end_time)
    for value in time_range.range(relativedelta(hours=+time_slice_in_hours)):
           x_time_slice_list.append(value)

    qset = Price.objects.filter(
        created__in= x_time_slice_list,
        created__minute=end_time.minute
    ).values('price')
    return [r['price'] for r in qset]

2

-1

Chad Lamb 4 年前

您可以通过在python中处理时间片过滤来实现这一点。

我的意思是,如果你接受你的函数。即

def _get_prices_per_time_slice(self, last_hours=24):
    now = timezone.now()
    end_time = now.replace(second = 0, microsecond = 0)
    start_time = end_time - timedelta(hours=last_hours)
    qset = Price.objects.filter(
        created__range=[start_time, end_time],
        created__minute=end_time.minute
    ).values('price')
    return [r['price'] for r in qset]

并按照如下方式重写它,以返回创建的数据并处理返回列表理解中的过滤。

def _get_prices_per_time_slice(self, last_hours=24, time_slice_in_hours=4):
    now = timezone.now()
    end_time = now.replace(second = 0, microsecond = 0)
    start_time = end_time - timedelta(hours=last_hours)
    qset = Price.objects.filter(
        created__range=[start_time, end_time],
        created__minute=end_time.minute
    ).values('price', 'created')
    return [r.get('price') for r in qset if r.get('created').hour % time_slice_in_hours == 0]