两个字段之间的时间增量 [英] Timedelta between two fields

问题描述

我正在寻找两个字段之间的时间间隔大于一定天数的对象。

I'm looking for objects where the timedelta between two fields is greater than a certain number of days.

Baiscally我有个发送信件的日期，以及获得批准的日期。假设在30天之内未收到批准，则这些对象应包含在查询集中。

Baiscally I have a date when a letter is sent, and a date when an approval is received. When no approval is received in let's say 30 days, then these objects should be included in the queryset.

我可以执行以下操作，其中增量是静态的。
但是我不需要 datetime.date.today（）作为开始，但需要与另一个对象进行比较。

I can do something like the below, where the delta is something static. However I don't need datetime.date.today() as a start but need to compare against the other object.

delta = datetime.date.today() - datetime.timedelta(30)
return qs.filter(letter_sent__isnull=False)\
    .filter(approval_from__isnull=True)\
    .filter(letter_sent__gte=delta)

任何指针该怎么做？

推荐答案

听起来像您想用 F 对象。像这样的东西：

Sounds like you want to annotate with an F object. Something like this:

from django.db.models import DateTimeField, ExpressionWrapper, F

delta = datetime.timedelta(days=30)
expression = F('approval_from') - F('letter_sent')
wrapped_expression = ExpressionWrapper(expression, DateTimeField())
qs = qs.objects.annotate(delta=wrapped_expression)
qs = qs.filter(delta__gte=delta)

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