Aggregation documentation should mention conditional aggregation

[Simon Willison]

I couldn't find a reference to ​https://docs.djangoproject.com/en/3.1/ref/models/conditional-expressions/#conditional-aggregation anywhere on ​https://docs.djangoproject.com/en/3.1/topics/db/aggregation/

[Simon Willison]

I found one mention here: ​https://docs.djangoproject.com/en/3.1/topics/db/aggregation/#filtering-on-annotations

[Mariusz Felisiak]

There is also an example in the ​Cheat sheet. A small reference should be enough, e.g.

diff --git a/docs/topics/db/aggregation.txt b/docs/topics/db/aggregation.txt
index cc6310052a..2e882e2a1a 100644
--- a/docs/topics/db/aggregation.txt
+++ b/docs/topics/db/aggregation.txt
@@ -354,7 +354,7 @@ authors with a count of highly rated books::
     >>> Author.objects.annotate(num_books=Count('book'), highly_rated_books=highly_rated)
 
 Each ``Author`` in the result set will have the ``num_books`` and
-``highly_rated_books`` attributes.
+``highly_rated_books`` attributes. See also :ref:`conditional-aggregation`.
 
 .. admonition:: Choosing between ``filter`` and ``QuerySet.filter()``

What do you think?

[GitHub <noreply@…>]

In 1351f2e:

Fixed #32618 -- Added link to conditional aggregation in aggregation topic guide.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 078bcd58:

[3.2.x] Fixed #32618 -- Added link to conditional aggregation in aggregation topic guide.

Backport of 1351f2ee163145df2cf5471eb3e57289f8853512 from main