Refs #35381 -- Delegated ArrayField element prepping to base_field.get_db_prep_save.

Previously, ArrayField always used base_field.get_db_prep_value when saving,
which could differ from how base_field prepares data for save. This change
overrides ArrayField.get_db_prep_save to delegate to the base_field's
get_db_prep_save, ensuring elements like None in JSONField arrays are saved
correctly as SQL NULL instead of JSON null.

django/contrib/postgres/fields/array.py

@@ -135,6 +135,11 @@ class ArrayField(CheckPostgresInstalledMixin, CheckFieldDefaultMixin, Field):
             ]
         return value
 
+    def get_db_prep_save(self, value, connection):
+        if isinstance(value, (list, tuple)):
+            return [self.base_field.get_db_prep_save(i, connection) for i in value]
+        return value
+
     def deconstruct(self):
         name, path, args, kwargs = super().deconstruct()
         if path == "django.contrib.postgres.fields.array.ArrayField":

docs/releases/6.1.txt

@@ -319,6 +319,15 @@ backends.
 
 * Support for PostGIS 3.1 is removed.
 
+:mod:`django.contrib.postgres`
+------------------------------
+
+* Top-level elements set to ``None`` in an
+  :class:`~django.contrib.postgres.fields.ArrayField` with a
+  :class:`~django.db.models.JSONField` base field are now saved as SQL ``NULL``
+  instead of the JSON ``null`` primitive. This matches the behavior of a
+  standalone :class:`~django.db.models.JSONField` when storing ``None`` values.
+
 Dropped support for PostgreSQL 14
 ---------------------------------
 

tests/postgres_tests/models.py

@@ -79,7 +79,7 @@ class OtherTypesArrayModel(PostgreSQLModel):
         models.DecimalField(max_digits=5, decimal_places=2), default=list
     )
     tags = ArrayField(TagField(), blank=True, null=True)
-    json = ArrayField(models.JSONField(default=dict), default=list)
+    json = ArrayField(models.JSONField(default=dict), default=list, null=True)
     int_ranges = ArrayField(IntegerRangeField(), blank=True, null=True)
     bigint_ranges = ArrayField(BigIntegerRangeField(), blank=True, null=True)
 

tests/postgres_tests/test_array.py

@@ -10,6 +10,7 @@ from django.core import checks, exceptions, serializers, validators
 from django.core.exceptions import FieldError
 from django.core.management import call_command
 from django.db import IntegrityError, connection, models
+from django.db.models import JSONNull
 from django.db.models.expressions import Exists, F, OuterRef, RawSQL, Value
 from django.db.models.functions import Cast, JSONObject, Upper
 from django.test import TransactionTestCase, override_settings, skipUnlessDBFeature
@@ -1577,3 +1578,29 @@ class TestAdminUtils(PostgreSQLTestCase):
             self.empty_value,
         )
         self.assertEqual(display_value, self.empty_value)
+
+
+class TestJSONFieldQuerying(PostgreSQLTestCase):
+    def test_saving_and_querying_for_sql_null(self):
+        obj = OtherTypesArrayModel.objects.create(json=[None, None])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__isnull=True), [obj]
+        )
+
+    def test_saving_and_querying_for_json_null(self):
+        obj = OtherTypesArrayModel.objects.create(json=[JSONNull(), JSONNull()])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1=JSONNull()), [obj]
+        )
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__isnull=True), []
+        )
+
+    def test_saving_and_querying_for_nested_json_nulls(self):
+        obj = OtherTypesArrayModel.objects.create(json=[[None, 1], [None, 2]])
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__0=None), [obj]
+        )
+        self.assertSequenceEqual(
+            OtherTypesArrayModel.objects.filter(json__1__0__isnull=True), []
+        )