python - 减去两个带注释的列

Question

我需要能够对两个带注释的列的聚合进行排序

所以我想做这样的事情:

c = c.annotate(metric=Sum('results__metric'))
c = c.annotate(metric_prior=Sum('results__metric_prior'))
c = c.annotate(variance=F('metric')-F('metric_prior')) #doesn't work, for demonstrative purposes only

然后:

c = c.order_by('variance')

有谁知道如何完成上述的事情？

Answer 1

其实

c = c.annotate(variance=F('metric')-F('metric_prior'))

works as you would like it to starting with Django 1.8 .

此外，您还可以通过表达式排序，这意味着您可以使用:

c = c.order_by(F('metric') - F('metric_prior'))

甚至只是:

c = c.order_by(Sum('results__metric') - Sum('results__metric_prior'))