[5.2.x] Fixed #35167 -- Delegated to super() in JSONField.get_db_prep_save().

Avoids reports of bulk_update() sending Cast expressions
to JSONField.get_prep_value().

Co-authored-by: Simon Charette <charette.s@gmail.com>

Backport of 0bf412111be686b6b23e00863f5d449d63557dbf from main.

django/db/models/fields/json.py

@@ -99,18 +99,23 @@ class JSONField(CheckFieldDefaultMixin, Field):
     def get_db_prep_value(self, value, connection, prepared=False):
         if not prepared:
             value = self.get_prep_value(value)
-        if isinstance(value, expressions.Value) and isinstance(
-            value.output_field, JSONField
-        ):
-            value = value.value
-        elif hasattr(value, "as_sql"):
-            return value
         return connection.ops.adapt_json_value(value, self.encoder)
 
     def get_db_prep_save(self, value, connection):
+        # This slightly involved logic is to allow for `None` to be used to
+        # store SQL `NULL` while `Value(None, JSONField())` can be used to
+        # store JSON `null` while preventing compilable `as_sql` values from
+        # making their way to `get_db_prep_value`, which is what the `super()`
+        # implementation does.
         if value is None:
             return value
-        return self.get_db_prep_value(value, connection)
+        if (
+            isinstance(value, expressions.Value)
+            and value.value is None
+            and isinstance(value.output_field, JSONField)
+        ):
+            value = None
+        return super().get_db_prep_save(value, connection)
 
     def get_transform(self, name):
         transform = super().get_transform(name)

tests/model_fields/models.py

@@ -430,6 +430,17 @@ class RelatedJSONModel(models.Model):
         required_db_features = {"supports_json_field"}
 
 
+class CustomSerializationJSONModel(models.Model):
+    class StringifiedJSONField(models.JSONField):
+        def get_prep_value(self, value):
+            return json.dumps(value, cls=self.encoder)
+
+    json_field = StringifiedJSONField()
+
+    class Meta:
+        required_db_features = {"supports_json_field"}
+
+
 class AllFieldsModel(models.Model):
     big_integer = models.BigIntegerField()
     binary = models.BinaryField()

tests/model_fields/test_jsonfield.py

@@ -40,7 +40,13 @@ from django.db.models.functions import Cast
 from django.test import SimpleTestCase, TestCase, skipIfDBFeature, skipUnlessDBFeature
 from django.test.utils import CaptureQueriesContext
 
-from .models import CustomJSONDecoder, JSONModel, NullableJSONModel, RelatedJSONModel
+from .models import (
+    CustomJSONDecoder,
+    CustomSerializationJSONModel,
+    JSONModel,
+    NullableJSONModel,
+    RelatedJSONModel,
+)
 
 
 @skipUnlessDBFeature("supports_json_field")
@@ -298,6 +304,17 @@ class TestSaveLoad(TestCase):
         obj.refresh_from_db()
         self.assertEqual(obj.value, value)
 
+    def test_bulk_update_custom_get_prep_value(self):
+        objs = CustomSerializationJSONModel.objects.bulk_create(
+            [CustomSerializationJSONModel(pk=1, json_field={"version": "1"})]
+        )
+        objs[0].json_field["version"] = "1-alpha"
+        CustomSerializationJSONModel.objects.bulk_update(objs, ["json_field"])
+        self.assertSequenceEqual(
+            CustomSerializationJSONModel.objects.values("json_field"),
+            [{"json_field": '{"version": "1-alpha"}'}],
+        )
+
 
 @skipUnlessDBFeature("supports_json_field")
 class TestQuerying(TestCase):