Refs #34551 -- Fixed QuerySet.aggregate() crash on precending aggrega…

…tion reference.

Regression in 1297c0d.

Refs #31679.

django/db/models/aggregates.py

@@ -65,7 +65,14 @@ def resolve_expression(
         c.filter = c.filter and c.filter.resolve_expression(
             query, allow_joins, reuse, summarize
         )
-        if not summarize:
+        if summarize:
+            # Summarized aggregates cannot refer to summarized aggregates.
+            for ref in c.get_refs():
+                if query.annotations[ref].is_summary:
+                    raise FieldError(
+                        f"Cannot compute {c.name}('{ref}'): '{ref}' is an aggregate"
+                    )
+        elif not self.is_summary:
             # Call Aggregate.get_source_expressions() to avoid
             # returning self.filter and including that in this loop.
             expressions = super(Aggregate, c).get_source_expressions()

django/db/models/sql/query.py

@@ -400,15 +400,27 @@ def get_aggregation(self, using, aggregate_exprs):
         """
         if not aggregate_exprs:
             return {}
-        aggregates = {}
+        # Store annotation mask prior to temporarily adding aggregations for
+        # resolving purpose to facilitate their subsequent removal.
+        replacements = {}
+        annotation_select_mask = self.annotation_select_mask
         for alias, aggregate_expr in aggregate_exprs.items():
             self.check_alias(alias)
             aggregate = aggregate_expr.resolve_expression(
                 self, allow_joins=True, reuse=None, summarize=True
             )
             if not aggregate.contains_aggregate:
                 raise TypeError("%s is not an aggregate expression" % alias)
-            aggregates[alias] = aggregate
+            # Temporarily add aggregate to annotations to allow remaining
+            # members of `aggregates` to resolve against each others.
+            self.append_annotation_mask([alias])
+            aggregate = aggregate.replace_expressions(replacements)
+            self.annotations[alias] = aggregate
+            replacements[Ref(alias, aggregate)] = aggregate
+        # Stash resolved aggregates now that they have been allowed to resolve
+        # against each other.
+        aggregates = {alias: self.annotations.pop(alias) for alias in aggregate_exprs}
+        self.set_annotation_mask(annotation_select_mask)
         # Existing usage of aggregation can be determined by the presence of
         # selected aggregates but also by filters against aliased aggregates.
         _, having, qualify = self.where.split_having_qualify()

docs/releases/4.2.2.txt

@@ -28,3 +28,7 @@ Bugfixes
 
 * Fixed a regression in Django 4.2 where nonexistent stylesheet was linked on a
   “Congratulations!” page (:ticket:`34588`).
+
+* Fixed a regression in Django 4.2 that caused a crash of
+  ``QuerySet.aggregate()`` with expressions referencing other aggregates
+  (:ticket:`34551`).

tests/aggregation/tests.py

@@ -1260,7 +1260,7 @@ def test_annotate_over_annotate(self):
         self.assertEqual(author.sum_age, other_author.sum_age)
 
     def test_aggregate_over_aggregate(self):
-        msg = "Cannot resolve keyword 'age_agg' into field."
+        msg = "Cannot compute Avg('age_agg'): 'age_agg' is an aggregate"
         with self.assertRaisesMessage(FieldError, msg):
             Author.objects.aggregate(
                 age_agg=Sum(F("age")),
@@ -2102,12 +2102,17 @@ def test_exists_extra_where_with_aggregate(self):
         )
         self.assertEqual(len(qs), 6)
 
-    def test_aggregation_over_annotation_shared_alias(self):
+    def test_multiple_aggregate_references(self):
+        aggregates = Author.objects.aggregate(
+            total_books=Count("book"),
+            coalesced_total_books=Coalesce("total_books", 0),
+        )
         self.assertEqual(
-            Publisher.objects.annotate(agg=Count("book__authors")).aggregate(
-                agg=Count("agg"),
-            ),
-            {"agg": 5},
+            aggregates,
+            {
+                "total_books": 10,
+                "coalesced_total_books": 10,
+            },
         )