如何使用Django queryset获取datetime_difference？

Question

我有3种型号：

class Store(models.Model):
    title = models.CharField(u'Store_Title', max_length=100)

class OrderExtra(models.Model):
    order = models.OneToOneField(Order, verbose_name=u'Order')
    store = models.ForeignKey(Store)

class Order(models.Model):
    code = models.IntegerField(u'Order_Code')
    datetime_begin = models.DateTimeField(null=True)
    datetime_end = models.DateTimeField(null=True)

我还有一个queryset，它返回我所有的商店以及每个商店的订单数：

qs = Order.objects.values('orderextra__store__title').annotate(orders_count=Count('code'))

结果，我得到：

qs[0] = {'orders_count': 500, 'orderextra__store__title': u'MyTestStore 1'}
qs[1] = {'orders_count': 200, 'orderextra__store__title': u'MyTestStore 2'}

我想要的是执行以下操作的orm queryset或本机sql查询：

对于'MyTestStore 1' ，有500订单，每个订单都有datetime_begin和datetime_end。 对于这500订单中的每个订单，我要计算差异： diff = datetime_end - datetime_begin 。 结果，我将得到500差异。 下一步是计算： diff1 + diff2 + diff3 + diff500 / 500 （从所有diff diff1 + diff2 + diff3 + diff500 / 500平均值）。 作为查询集的最终结果，我想得到：

qs[0] = {'orders_average_diff': 7.3 (minutes), 'orderextra__store__title': u'MyTestStore 1'}
qs[1] = {'orders_average_diff': 4.2 (minutes), 'orderextra__store__title': u'MyTestStore 2'}

有没有办法做到这一点？ 谢谢。

Answer 1

为您提供正确的结果（结果可能采用不同的格式），请检查此项目

我不确定btw :)

z = {}
q1 = OrderExtra.objects.all()
for q in q1:
  # Get time difference in minutes for this order
  diff = q.order.datetime_end - q.order.datetime_begin
  diffm = diff.seconds / 60
  #check if store is already updated to z
  check = z.get(q.store.title, 'error')
  # if NOT add storeName as key and c= Counter, a = Avg date-time diff
  if check == 'error':
    z.update({q.store.title:{'c':1, 'd':diffm, 'a': diffm}})
  # If Available calculate avg with counter and total diff
  else:
    avgm = (( diffm + z[q.store.title]['d'] ) // (z[q.store.title]['c'] + 1))
    z[q.store.title]['a'] = avgm 
    z[q.store.title]['d'] = diffm + z[q.store.title]['d'] 
    z[q.store.title]['c'] =  z[q.store.title]['c'] + 1