在 Django 模型中使用 Greatest 函数时如何获取注释中的相关对象列表

Question

I am having two models, a User model and a Payment model and there is on to many relationship between them. User has multiple Payment s. What I am trying to achieve is sorting the User model as per the Payment 's created_at field.

I am trying to modify the Queryset and then I'll be using the annotated field latest_tran for sorting.

def get_queryset(self, request):
    qs = super(ClubbedPaymentAdmin, self).get_queryset(request)
    qs = qs.annotate(
        latest_tran=Greatest(Payment.objects.filter(user=F('id')).values_list('created_at', flat=True)))
    return qs

But I am having below error.

Greatest must take at least two expressions

So it seems like I am making a mistake when evaluating the list of Payment s. Or may be like I am taking a wrong approach. Any help would be much appreciated. Thank you.

Edit

I am using the default User model for users which are there in django

My Payment model looks like this -

class Payment(models.Model):
    amount = models.FloatField('Points', max_length=10)
    purchase_token = models.TextField(max_length=250)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    note = models.TextField(max_length=1000, default=None, blank=True)
    created_at = models.DateTimeField('Transaction Date')
    updated_at = models.DateTimeField('Updated at', auto_now=True)

Answer 1

Greatest does not take the maximum, it takes the largest of the different parameters , so Greatest('foo', 'bar') will take the largest of the foo and bar column.

What you need isMax [Django-doc] . You can make use of the name separated by an underscore, so:

from django.db.models import 

def get_queryset(self, *args, **kwargs):
    return super().get_queryset(*args, **kwargs).annotate(
        
    )

---

Note : It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation .

Answer 2

Something like this, using theMax(...) ?

from django.db.models import Max


def get_queryset(self, request):
    qs = super(ClubbedPaymentAdmin, self).get_queryset(request)
    qs = qs.annotate(latest_tran=)
    return qs