[4.2.x] Fixed #34285 -- Fixed index/slice lookups on filtered aggregates with ArrayField.

Thanks Simon Charette for the review.

Backport of ae1fe72e9b1f5fe3b05e5b670bd0c205cd305e71 from main

2 files changed, 49 insertions, 2 deletions

diff --git a/django/contrib/postgres/fields/array.py b/django/contrib/postgres/fields/array.py
index 8477dd9fff..c8e8e132e0 100644
--- a/django/contrib/postgres/fields/array.py
+++ b/django/contrib/postgres/fields/array.py
@@ -325,7 +325,9 @@ class IndexTransform(Transform):
 
     def as_sql(self, compiler, connection):
         lhs, params = compiler.compile(self.lhs)
-        return "%s[%%s]" % lhs, params + [self.index]
+        if not lhs.endswith("]"):
+            lhs = "(%s)" % lhs
+        return "%s[%%s]" % lhs, (*params, self.index)
 
     @property
     def output_field(self):
@@ -349,7 +351,9 @@ class SliceTransform(Transform):
 
     def as_sql(self, compiler, connection):
         lhs, params = compiler.compile(self.lhs)
-        return "%s[%%s:%%s]" % lhs, params + [self.start, self.end]
+        if not lhs.endswith("]"):
+            lhs = "(%s)" % lhs
+        return "%s[%%s:%%s]" % lhs, (*params, self.start, self.end)
 
 
 class SliceTransformFactory:
diff --git a/tests/postgres_tests/test_aggregates.py b/tests/postgres_tests/test_aggregates.py
index b5474d361e..e781fd87ee 100644
--- a/tests/postgres_tests/test_aggregates.py
+++ b/tests/postgres_tests/test_aggregates.py
@@ -365,6 +365,49 @@ class TestGeneralAggregate(PostgreSQLTestCase):
         )
         self.assertCountEqual(qs.get(), [1, 2])
 
+    def test_array_agg_filter_index(self):
+        aggr1 = AggregateTestModel.objects.create(integer_field=1)
+        aggr2 = AggregateTestModel.objects.create(integer_field=2)
+        StatTestModel.objects.bulk_create(
+            [
+                StatTestModel(related_field=aggr1, int1=1, int2=0),
+                StatTestModel(related_field=aggr1, int1=2, int2=1),
+                StatTestModel(related_field=aggr2, int1=3, int2=0),
+                StatTestModel(related_field=aggr2, int1=4, int2=1),
+            ]
+        )
+        qs = (
+            AggregateTestModel.objects.filter(pk__in=[aggr1.pk, aggr2.pk])
+            .annotate(
+                array=ArrayAgg("stattestmodel__int1", filter=Q(stattestmodel__int2=0))
+            )
+            .annotate(array_value=F("array__0"))
+            .values_list("array_value", flat=True)
+        )
+        self.assertCountEqual(qs, [1, 3])
+
+    def test_array_agg_filter_slice(self):
+        aggr1 = AggregateTestModel.objects.create(integer_field=1)
+        aggr2 = AggregateTestModel.objects.create(integer_field=2)
+        StatTestModel.objects.bulk_create(
+            [
+                StatTestModel(related_field=aggr1, int1=1, int2=0),
+                StatTestModel(related_field=aggr1, int1=2, int2=1),
+                StatTestModel(related_field=aggr2, int1=3, int2=0),
+                StatTestModel(related_field=aggr2, int1=4, int2=1),
+                StatTestModel(related_field=aggr2, int1=5, int2=0),
+            ]
+        )
+        qs = (
+            AggregateTestModel.objects.filter(pk__in=[aggr1.pk, aggr2.pk])
+            .annotate(
+                array=ArrayAgg("stattestmodel__int1", filter=Q(stattestmodel__int2=0))
+            )
+            .annotate(array_value=F("array__1_2"))
+            .values_list("array_value", flat=True)
+        )
+        self.assertCountEqual(qs, [[], [5]])
+
     def test_bit_and_general(self):
         values = AggregateTestModel.objects.filter(integer_field__in=[0, 1]).aggregate(
             bitand=BitAnd("integer_field")