Issue
I have a model Client
, how do i annotate then sort, the Max of its two fields:
from django.db import models
class Client(models.Model):
uploaded_photo_at = models.DateTimeField()
uploaded_document_at = models.DateTimeField()
The following:
Client.objects.annotate(
latest_activity_at=Max('uploaded_photo_at', 'uploaded_document_at', output_field=DateTimeField())
).order_by('latest_activity_at')
Raises this error:
django.db.utils.ProgrammingError: function max(timestamp with time zone, timestamp with time zone) does not exist
LINE 1: ...oto_at", "clients_client"."uploaded_document_at", MAX("clien...
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
I am using Posgresql and Django 1.11, if that helps.
Solution
Thanks to Robert's answer i was able to find Greatest
class of Django.
The following works:
from django.db.models.functions import Greatest
Client.objects.annotate(
latest_activity_at=Greatest('uploaded_photo_at', 'uploaded_document_at')
).order_by('latest_activity_at')
Answered By - A. K. Tolentino
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