Django:按月计数对象 [英] Django: Count objects by month

问题描述

我研究了Django文档，并尝试了许多示例，但是它实际上并不容易，尽管实际上应该很简单.

I studied the Django docu and tried many examples but it still doesn't work, though it should be very easy, actually.

这是我的模特

class Dummy(models.Model):
    timestamp = models.DateTimeField()

我有一些示例对象，可以像这样通过外壳列出:

I have some sample objects which I am able to list via the shell like that:

% python manage.py shell
Python 3.7.7 (default, Mar 10 2020, 15:43:33) 
[Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from conv.models import Dummy
>>> dummy = Dummy.objects.order_by('timestamp')
>>> for d in dummy:
...     print(d.id, d.timestamp)

6 2019-05-01 07:00:06+00:00
4 2020-04-01 22:00:00+00:00
5 2020-04-15 04:00:00+00:00
1 2020-05-17 09:42:00+00:00
2 2020-05-18 09:42:15+00:00
3 2020-05-19 09:42:21+00:00
>>>

现在，我想按年/月计数对象.仅按年份过滤:

Now I want to count the objects by year / month. Filtering by year only works:

>>> Dummy.objects.filter(timestamp__year='2020').count()
5

但是按月过滤不起作用:

But filtering by month doesn't work:

>>> Dummy.objects.filter(timestamp__month='5').count()
0

实际上结果应该是4.怎么了?

Actually the result should be 4. What's wrong?

推荐答案

我使用的MySQL-DB出现了一些麻烦，与

There was some trouble with the MySQL-DB I was using very similar to this topic. When I switched back to SQLite I got the correct result:

>>> Dummy.objects.filter(timestamp__month='5').count()
4

现在，我还可以像这样将年份和月份的过滤组合在一起:

Now I also can combine filtering for year and month like that:

>>> Dummy.objects.filter(timestamp__year='2020', timestamp__month='5').count()
3

感谢 Willem Van Onsem的慷慨帮助我现在看到的事情更加清楚了，并且了解了很多有关TruncMonth和ExtractMonth的知识.似乎也是非常有用的工具.

Thanks to the generous help of Willem Van Onsem I see things clearer now and learned a lot about TruncMonth and ExtractMonth which seems to be very useful tools too.

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