[2.2.x] Fixed #30315 -- Fixed crash of ArrayAgg and StringAgg with ordering when used in Subquery.

Backport of a3f91891d2 from master.

django/contrib/postgres/aggregates/mixins.py

@@ -33,6 +33,12 @@ class OrderableAggMixin:
             return sql, sql_params + ordering_params
         return super().as_sql(compiler, connection, ordering='')
 
+    def set_source_expressions(self, exprs):
+        # Extract the ordering expressions because ORDER BY clause is handled
+        # in a custom way.
+        self.ordering = exprs[self._get_ordering_expressions_index():]
+        return super().set_source_expressions(exprs[:self._get_ordering_expressions_index()])
+
     def get_source_expressions(self):
         return self.source_expressions + self.ordering
 

docs/releases/2.2.2.txt

@@ -21,3 +21,7 @@ Bugfixes
 
 * Fixed a regression in Django 2.2 where auto-reloader doesn't detect changes
   in ``manage.py`` file when using ``StatReloader`` (:ticket:`30479`).
+
+* Fixed crash of :class:`~django.contrib.postgres.aggregates.ArrayAgg` and
+  :class:`~django.contrib.postgres.aggregates.StringAgg` with ``ordering``
+  argument when used in a ``Subquery`` (:ticket:`30315`).

tests/postgres_tests/test_aggregates.py

@@ -1,7 +1,8 @@
 import json
 
-from django.db.models.expressions import F, Value
-from django.db.models.functions import Concat, Substr
+from django.db.models import CharField
+from django.db.models.expressions import F, OuterRef, Subquery, Value
+from django.db.models.functions import Cast, Concat, Substr
 from django.test.testcases import skipUnlessDBFeature
 from django.test.utils import Approximate
 
@@ -203,6 +204,36 @@ class TestGeneralAggregate(PostgreSQLTestCase):
         values = AggregateTestModel.objects.none().aggregate(jsonagg=JSONBAgg('integer_field'))
         self.assertEqual(values, json.loads('{"jsonagg": []}'))
 
+    def test_string_agg_array_agg_ordering_in_subquery(self):
+        stats = []
+        for i, agg in enumerate(AggregateTestModel.objects.order_by('char_field')):
+            stats.append(StatTestModel(related_field=agg, int1=i, int2=i + 1))
+            stats.append(StatTestModel(related_field=agg, int1=i + 1, int2=i))
+        StatTestModel.objects.bulk_create(stats)
+
+        for aggregate, expected_result in (
+            (
+                ArrayAgg('stattestmodel__int1', ordering='-stattestmodel__int2'),
+                [('Foo1', [0, 1]), ('Foo2', [1, 2]), ('Foo3', [2, 3]), ('Foo4', [3, 4])],
+            ),
+            (
+                StringAgg(
+                    Cast('stattestmodel__int1', CharField()),
+                    delimiter=';',
+                    ordering='-stattestmodel__int2',
+                ),
+                [('Foo1', '0;1'), ('Foo2', '1;2'), ('Foo3', '2;3'), ('Foo4', '3;4')],
+            ),
+        ):
+            with self.subTest(aggregate=aggregate.__class__.__name__):
+                subquery = AggregateTestModel.objects.filter(
+                    pk=OuterRef('pk'),
+                ).annotate(agg=aggregate).values('agg')
+                values = AggregateTestModel.objects.annotate(
+                    agg=Subquery(subquery),
+                ).order_by('char_field').values_list('char_field', 'agg')
+                self.assertEqual(list(values), expected_result)
+
 
 class TestAggregateDistinct(PostgreSQLTestCase):
     @classmethod