Refs #26511 -- Fixed json.KeyTextTransform() on MySQL/MariaDB.

django/db/models/fields/json.py

@@ -4,6 +4,7 @@ from django import forms
 from django.core import checks, exceptions
 from django.db import NotSupportedError, connections, router
 from django.db.models import lookups
+from django.db.models.fields import TextField
 from django.db.models.lookups import PostgresOperatorLookup, Transform
 from django.utils.translation import gettext_lazy as _
 
@@ -366,6 +367,17 @@ class KeyTransform(Transform):
 class KeyTextTransform(KeyTransform):
     postgres_operator = "->>"
     postgres_nested_operator = "#>>"
+    output_field = TextField()
+
+    def as_mysql(self, compiler, connection):
+        if connection.mysql_is_mariadb:
+            # MariaDB doesn't support -> and ->> operators (see MDEV-13594).
+            sql, params = super().as_mysql(compiler, connection)
+            return "JSON_UNQUOTE(%s)" % sql, params
+        else:
+            lhs, params, key_transforms = self.preprocess_lhs(compiler, connection)
+            json_path = compile_json_path(key_transforms)
+            return "(%s ->> %%s)" % lhs, tuple(params) + (json_path,)
 
 
 class KeyTransformTextLookupMixin:

tests/model_fields/test_jsonfield.py

@@ -370,6 +370,7 @@ class TestQuerying(TestCase):
             ).order_by("key"),
         ):
             self.assertSequenceEqual(qs, [self.objs[4]])
+        none_val = "" if connection.features.interprets_empty_strings_as_nulls else None
         qs = NullableJSONModel.objects.filter(value__isnull=False)
         self.assertQuerysetEqual(
             qs.filter(value__isnull=False)
@@ -381,7 +382,7 @@ class TestQuerying(TestCase):
             .values("key")
             .annotate(count=Count("key"))
             .order_by("count"),
-            [(None, 0), ("g", 1)],
+            [(none_val, 0), ("g", 1)],
             operator.itemgetter("key", "count"),
         )
 
@@ -494,6 +495,17 @@ class TestQuerying(TestCase):
             [self.objs[4]],
         )
 
+    def test_key_text_transform_char_lookup(self):
+        qs = NullableJSONModel.objects.annotate(
+            char_value=KeyTextTransform("foo", "value"),
+        ).filter(char_value__startswith="bar")
+        self.assertSequenceEqual(qs, [self.objs[7]])
+
+        qs = NullableJSONModel.objects.annotate(
+            char_value=KeyTextTransform(1, KeyTextTransform("bar", "value")),
+        ).filter(char_value__startswith="bar")
+        self.assertSequenceEqual(qs, [self.objs[7]])
+
     def test_expression_wrapper_key_transform(self):
         self.assertCountEqual(
             NullableJSONModel.objects.annotate(