如何使用两个字段作为组合字段对Django queryset进行排序

Question

I have a Deadline model which have two fields, start_date and end_date . I want to sort the queryset with both the fields but have a copy of deadline for each date

I tried creating annotated common fields and ordering through that.

class Deadline(models.Model):
    start_date = models.DateTimeField()
    end_date = models.DateTimeField

dl_start = deadline_queryset.annotate(date=F('start_date'))
dl_end = deadlien_queryset.annotate(date=F('end_date'))
dl_all = dl_start.union(dl_end).order_by('date')

I need a timeline of events.
Consider if my queryset has 2 objects:

Deadline <id: 1, start_date: 12-dec, end_date: 24-jan>
Deadline <id: 2, start_date: 15-dec, end_date: 21-jan>

I need a list of deadlines like:

Deadline <id: 1, start_date: 12-dec, end_date: 24-jan, date: 12-dec>
Deadline <id: 2, start_date: 15-dec, end_date: 21-jan, date: 15-dec>
Deadline <id: 2, start_date: 15-dec, end_date: 21-jan, date: 21-jan>
Deadline <id: 1, start_date: 12-dec, end_date: 24-jan, date: 24-jan>

Answer 1

In my aforementioned code, the annotated fields were not being carry forward after the union and so I was unable to use order_by on it.

It worked after using the following variation:

dl_start = deadline_queryset.annotate(date=F('start_date')).values('id', 'start_date', 'end_date', 'date')
dl_end = deadlien_queryset.annotate(date=F('end_date')).values('id', 'start_date', 'end_date', 'date')
dl_all = dl_start.union(dl_end).order_by('date')

This helped me carry forward the annotated date field.