Refs #35381 -- Deprecated using None in JSONExact rhs to mean JSON null.

Key and index lookups are exempt from the deprecation.

Co-authored-by: Jacob Walls <jacobtylerwalls@gmail.com>

django/db/models/fields/json.py

@@ -1,4 +1,5 @@
 import json
+import warnings
 
 from django import forms
 from django.core import checks, exceptions
@@ -11,6 +12,7 @@ from django.db.models.lookups import (
     PostgresOperatorLookup,
     Transform,
 )
+from django.utils.deprecation import RemovedInDjango70Warning, django_file_prefixes
 from django.utils.translation import gettext_lazy as _
 
 from . import Field
@@ -332,10 +334,24 @@ class CaseInsensitiveMixin:
 
 
 class JSONExact(lookups.Exact):
+    # RemovedInDjango70Warning: When the deprecation period is over, remove
+    # the following line.
     can_use_none_as_rhs = True
 
     def process_rhs(self, compiler, connection):
+        if self.rhs is None and not isinstance(self.lhs, KeyTransform):
+            warnings.warn(
+                "Using None as the right-hand side of an exact lookup on JSONField to "
+                "mean JSON scalar 'null' is deprecated. Use JSONNull() instead (or use "
+                "the __isnull lookup if you meant SQL NULL).",
+                RemovedInDjango70Warning,
+                skip_file_prefixes=django_file_prefixes(),
+            )
+
         rhs, rhs_params = super().process_rhs(compiler, connection)
+
+        # RemovedInDjango70Warning: When the deprecation period is over, remove
+        # The following if-block entirely.
         # Treat None lookup values as null.
         if rhs == "%s" and (*rhs_params,) == (None,):
             rhs_params = ("null",)
@@ -547,6 +563,10 @@ class KeyTransformIn(lookups.In):
 
 
 class KeyTransformExact(JSONExact):
+    # RemovedInDjango70Warning: When deprecation period ends, uncomment the
+    # flag below.
+    # can_use_none_as_rhs = True
+
     def process_rhs(self, compiler, connection):
         if isinstance(self.rhs, KeyTransform):
             return super(lookups.Exact, self).process_rhs(compiler, connection)

docs/releases/6.1.txt

@@ -360,6 +360,13 @@ Miscellaneous
   is deprecated. Pass an explicit field name, like
   ``values_list("pk", flat=True)``.
 
+* The use of ``None`` to represent a top-level JSON scalar ``null`` when
+  querying :class:`~django.db.models.JSONField` is now deprecated in favor of
+  the new :class:`~django.db.models.JSONNull` expression. At the end
+  of the deprecation period, ``None`` values compile to SQL ``IS NULL`` when
+  used as the top-level value. :lookup:`Key and index lookups <jsonfield.key>`
+  are unaffected by this deprecation.
+
 Features removed in 6.1
 =======================
 

docs/topics/db/queries.txt

@@ -1069,6 +1069,11 @@ as JSON ``null``.
 When querying, :lookup:`isnull=True <isnull>` is used to match SQL ``NULL``,
 while exact-matching ``JSONNull()`` is used to match JSON ``null``.
 
+.. deprecated:: 6.1
+
+    Exact-matching ``None`` in a query to mean JSON ``null`` is deprecated.
+    After the deprecation period, it will be interpreted as SQL ``NULL``.
+
 .. versionchanged:: 6.1
 
     ``JSONNull()`` expression was added.
@@ -1080,6 +1085,12 @@ while exact-matching ``JSONNull()`` is used to match JSON ``null``.
     <Dog: Max>
     >>> Dog.objects.create(name="Archie", data=JSONNull())  # JSON null.
     <Dog: Archie>
+    >>> Dog.objects.filter(data=None)
+    ...: RemovedInDjango70Warning: Using None as the right-hand side of an
+    exact lookup on JSONField to mean JSON scalar 'null' is deprecated. Use
+    JSONNull() instead (or use the __isnull lookup if you meant SQL NULL).
+    ...
+    <QuerySet [<Dog: Archie>]>
     >>> Dog.objects.filter(data=JSONNull())
     <QuerySet [<Dog: Archie>]>
     >>> Dog.objects.filter(data__isnull=True)
@@ -1087,6 +1098,9 @@ while exact-matching ``JSONNull()`` is used to match JSON ``null``.
     >>> Dog.objects.filter(data__isnull=False)
     <QuerySet [<Dog: Archie>]>
 
+.. RemovedInDjango70Warning: Alter the example with the deprecation warning to:
+  <QuerySet [<Dog: Max>]>.
+
 Unless you are sure you wish to work with SQL ``NULL`` values, consider setting
 ``null=False`` and providing a suitable default for empty values, such as
 ``default=dict``.

tests/model_fields/test_jsonfield.py

@@ -41,8 +41,15 @@ from django.db.models.fields.json import (
     KeyTransformTextLookupMixin,
 )
 from django.db.models.functions import Cast
-from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature
+from django.test import (
+    SimpleTestCase,
+    TestCase,
+    ignore_warnings,
+    skipIfDBFeature,
+    skipUnlessDBFeature,
+)
 from django.test.utils import CaptureQueriesContext
+from django.utils.deprecation import RemovedInDjango70Warning
 
 from .models import (
     CustomJSONDecoder,
@@ -229,6 +236,8 @@ class TestSaveLoad(TestCase):
         self.assertIsNone(obj.value)
 
     @skipUnlessDBFeature("supports_primitives_in_json_field")
+    # RemovedInDjango70Warning.
+    @ignore_warnings(category=RemovedInDjango70Warning)
     def test_json_null_different_from_sql_null(self):
         json_null = NullableJSONModel.objects.create(value=Value(None, JSONField()))
         NullableJSONModel.objects.update(value=Value(None, JSONField()))
@@ -242,6 +251,9 @@ class TestSaveLoad(TestCase):
         )
         self.assertSequenceEqual(
             NullableJSONModel.objects.filter(value=None),
+            # RemovedInDjango70Warning: When the deprecation ends, replace
+            # with:
+            # [sql_null],
             [json_null],
         )
         self.assertSequenceEqual(
@@ -1365,3 +1377,36 @@ class JSONNullTests(TestCase):
         obj.refresh_from_db()
         self.assertIsNone(obj.value["name"])
         self.assertEqual(obj.value["array"], [1, None])
+
+
+# RemovedInDjango70Warning.
+@skipUnlessDBFeature("supports_primitives_in_json_field")
+class JSONExactNoneDeprecationTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.msg = (
+            "Using None as the right-hand side of an exact lookup on JSONField to mean "
+            "JSON scalar 'null' is deprecated. Use JSONNull() instead (or use the "
+            "__isnull lookup if you meant SQL NULL)."
+        )
+        cls.obj = NullableJSONModel.objects.create(value=JSONNull())
+
+    def test_filter(self):
+        with self.assertWarnsMessage(RemovedInDjango70Warning, self.msg):
+            self.assertSequenceEqual(
+                NullableJSONModel.objects.filter(value=None), [self.obj]
+            )
+
+    def test_annotation_q_filter(self):
+        qs = NullableJSONModel.objects.annotate(
+            has_empty_data=Q(value__isnull=True) | Q(value=None)
+        ).filter(has_empty_data=True)
+        with self.assertWarnsMessage(RemovedInDjango70Warning, self.msg):
+            self.assertSequenceEqual(qs, [self.obj])
+
+    def test_case_when(self):
+        qs = NullableJSONModel.objects.annotate(
+            has_json_null=Case(When(value=None, then=Value(True)), default=Value(False))
+        ).filter(has_json_null=True)
+        with self.assertWarnsMessage(RemovedInDjango70Warning, self.msg):
+            self.assertSequenceEqual(qs, [self.obj])

tests/postgres_tests/test_array.py

@@ -16,6 +16,7 @@ from django.db.models.functions import Cast, JSONObject, Upper
 from django.test import TransactionTestCase, override_settings, skipUnlessDBFeature
 from django.test.utils import isolate_apps
 from django.utils import timezone
+from django.utils.deprecation import RemovedInDjango70Warning
 
 from . import PostgreSQLSimpleTestCase, PostgreSQLTestCase, PostgreSQLWidgetTestCase
 from .models import (
@@ -1586,6 +1587,17 @@ class TestJSONFieldQuerying(PostgreSQLTestCase):
         self.assertSequenceEqual(
             OtherTypesArrayModel.objects.filter(json__1__isnull=True), [obj]
         )
+        # RemovedInDjango70Warning.
+        msg = (
+            "Using None as the right-hand side of an exact lookup on JSONField to mean "
+            "JSON scalar 'null' is deprecated. Use JSONNull() instead (or use the "
+            "__isnull lookup if you meant SQL NULL)."
+        )
+        with self.assertWarnsMessage(RemovedInDjango70Warning, msg):
+            # RemovedInDjango70Warning: deindent, and replace [] with [obj].
+            self.assertSequenceEqual(
+                OtherTypesArrayModel.objects.filter(json__1=None), []
+            )
 
     def test_saving_and_querying_for_json_null(self):
         obj = OtherTypesArrayModel.objects.create(json=[JSONNull(), JSONNull()])