From c9b9a52edc66be117c6e5b5214fa788a4d5db7a8 Mon Sep 17 00:00:00 2001
From: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Date: Tue, 1 Aug 2023 16:16:28 +0200
Subject: [PATCH] Fixed #34750 -- Fixed QuerySet.count() when grouping by
 unused multi-valued annotations.

Thanks Toan Vuong for the report.
Thanks Simon Charette for the review.

Regression in 59bea9efd2768102fc9d3aedda469502c218e9b7.
---
 django/db/models/sql/query.py |  5 +++++
 docs/releases/4.2.4.txt       |  4 ++++
 tests/aggregation/tests.py    | 41 +++++++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index ac735012f11..220ae92754d 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -498,6 +498,11 @@ class Query(BaseExpression):
                             annotation_mask |= expr.get_refs()
                     for aggregate in aggregates.values():
                         annotation_mask |= aggregate.get_refs()
+                    # Avoid eliding expressions that might have an incidence on
+                    # the implicit grouping logic.
+                    for annotation_alias, annotation in self.annotation_select.items():
+                        if annotation.get_group_by_cols():
+                            annotation_mask.add(annotation_alias)
                     inner_query.set_annotation_mask(annotation_mask)
 
             # Add aggregates to the outer AggregateQuery. This requires making
diff --git a/docs/releases/4.2.4.txt b/docs/releases/4.2.4.txt
index a39818e3b87..9e3c2fc1fd7 100644
--- a/docs/releases/4.2.4.txt
+++ b/docs/releases/4.2.4.txt
@@ -15,3 +15,7 @@ Bugfixes
 
 * Fixed a regression in Django 4.2 that caused a crash when grouping by a
   reference in a subquery (:ticket:`34748`).
+
+* Fixed a regression in Django 4.2 that caused aggregation over query that
+  uses explicit grouping by multi-valued annotations to group against the wrong
+  columns (:ticket:`34750`).
diff --git a/tests/aggregation/tests.py b/tests/aggregation/tests.py
index 9f2a7c88418..ad00afdcc12 100644
--- a/tests/aggregation/tests.py
+++ b/tests/aggregation/tests.py
@@ -2165,6 +2165,47 @@ class AggregateAnnotationPruningTests(TestCase):
         self.assertEqual(sql.count("select"), 2, "Subquery wrapping required")
         self.assertNotIn("authors_count", sql)
 
+    def test_unused_aliased_aggregate_and_annotation_reverse_fk(self):
+        Book.objects.create(
+            name="b3",
+            publisher=self.p2,
+            pages=1000,
+            rating=4.2,
+            price=50,
+            contact=self.a2,
+            pubdate=datetime.date.today(),
+        )
+        qs = Publisher.objects.annotate(
+            total_pages=Sum("book__pages"),
+            good_book=Case(
+                When(book__rating__gt=4.0, then=Value(True)),
+                default=Value(False),
+            ),
+        )
+        self.assertEqual(qs.count(), 3)
+
+    def test_unused_aliased_aggregate_and_annotation_reverse_fk_grouped(self):
+        Book.objects.create(
+            name="b3",
+            publisher=self.p2,
+            pages=1000,
+            rating=4.2,
+            price=50,
+            contact=self.a2,
+            pubdate=datetime.date.today(),
+        )
+        qs = (
+            Publisher.objects.values("id", "name")
+            .annotate(total_pages=Sum("book__pages"))
+            .annotate(
+                good_book=Case(
+                    When(book__rating__gt=4.0, then=Value(True)),
+                    default=Value(False),
+                )
+            )
+        )
+        self.assertEqual(qs.count(), 3)
+
     def test_non_aggregate_annotation_pruned(self):
         with CaptureQueriesContext(connection) as ctx:
             Book.objects.annotate(