Question

i have a model Complaint with get_latest_response method

class Complaint(models.Model):
    message         = models.TextField(blank=True)
    email           = models.CharField(max_length=255)

    def get_latest_response(self):
        return ResponseLetter.objects.filter(complaint=self)[:1][0]

method get_latest_response return the latest respone to this complaint

and ResponseLetter model

class ResponseLetter(models.Model): 
    date_response       = models.DateField(db_index=True)
    response_content    = models.TextField()
    response_from       = models.CharField(max_length=255)

    complaint           = models.ForeignKey(Complaint)

    class Meta:
        ordering = ["-date_response"]

then in view i get complaints (queryset)

complaints = Complaint.objects.all()

and i have to order these complaints by get_latest_response().date_response

but! i cant convert this queryset to list like

complaints = list(complaints)
complaints.sort(key=lambda x: x.get_latest_response().date_response)

because after that i render this queryset in object_list :

return object_list(request, template_name = 'complaint/complaints.html',
        queryset = complaints, paginate_by = COMPLAINTS_PAGE_SIZE,
        extra_context=extra_context
    )

also method :

sorted(complaints, key=lambda a: a.get_latest_response().date_response)

doesnt work too

can you give me any advice please ?

Answer 1

You want to list Complaints ordered by ResponseLetter.date_response. But order_by and distinct don’t play well together. Here’s a workaround:

from django.db.models import Max

Complaint.objects.annotate(max=Max('responseletter__date_response')).order_by('-max')

Tested/working.