Django对象order_by给我重复的用户

Question

I am trying to get all users (excepted request.user ) and order them by datetime of last message they received. Maybe I am doing it wrong.

@login_required
def get_users(request):
    if request.method == 'POST':
        users = list(User.objects.filter(~Q(username = request.user))
            .order_by('personal_messages__sent_date').values())
        return HttpResponse(dumps({'users': users}))
    return redirect('message:index')

dumps is from json_tricks. Data are received by a Vue.js object with JS fetch
My models.py

from django.db import models
from django.conf import settings

    class PersonalMessage(models.Model):
        text = models.TextField()
        sender = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='personal_messages', null=True, on_delete=models.SET_NULL)
        recipient = models.ForeignKey(settings.AUTH_USER_MODEL, null=True, on_delete=models.SET_NULL)
        sent_date = models.DateTimeField('sent date', auto_now_add=True)

The thing is if I only do users = list(User.objects.filter(~Q(username = request.user)).values()) it works well but if I add the order_by users = list(User.objects.filter(~Q(username = request.user)) .order_by('personal_messages__sent_date').values()) I get duplicates for each user. Seems it returns each user n times if user is linked with n messages.
Maybe there is another way.
Any Idea?

Answer 1

You need to use aggregation and the query looks like this:

User.objects.filter(
    ~Q(username = request.user)
).annotate(
    last_message_sent_date=Max('personal_messages__sent_date')
).order_by(
    'last_message_sent_date'
)