Django 3.2 LTS Expressions can reference transforms

See also

• https://docs.djangoproject.com/en/dev/topics/db/queries/#using-transforms-in-expressions

• https://github.com/django/django/commit/83fcfc9ec8610540948815e127101f1206562ead

Expressions can reference transforms

New in Django 3.2.

Django supports using transforms in expressions.

For example, to find all Entry objects published in the same year as they were last modified:

>>> Entry.objects.filter(pub_date__year=F('mod_date__year'))

To find the earliest year an entry was published, we can issue the query:

>>> Entry.objects.aggregate(first_published_year=Min('pub_date__year'))

This example finds the value of the highest rated entry and the total number of comments on all entries for each year:

>>> Entry.objects.values('pub_date__year').annotate(
...     top_rating=Subquery(
...         Entry.objects.filter(
...             pub_date__year=OuterRef('pub_date__year'),
...         ).order_by('-rating').values('rating')[:1]
...     ),
...     total_comments=Sum('number_of_comments'),
... )