Fixed #36085 -- Added JSONField support for negative array indexing on SQLite.

Author: savanto

django/db/backends/base/features.py

@@ -347,6 +347,8 @@ class BaseDatabaseFeatures:
     json_key_contains_list_matching_requires_list = False
     # Does the backend support JSONObject() database function?
     has_json_object_function = True
+    # Does the backend support negative JSON array indexing?
+    supports_json_negative_indexing = True
 
     # Does the backend support column collations?
     supports_collation_on_charfield = True

django/db/backends/base/operations.py

@@ -793,6 +793,12 @@ def format_debug_sql(self, sql):
         # Hook for backends (e.g. NoSQL) to customize formatting.
         return sqlparse.format(sql, reindent=True, keyword_case="upper")
 
+    def format_json_path_numeric_index(self, num):
+        """
+        Hook for backends to customize array indexing in JSON paths.
+        """
+        return "[%s]" % num
+
     def compile_json_path(self, key_transforms, include_root=True):
         """
         Hook for backends to customize all aspects of JSON path construction.
@@ -805,5 +811,13 @@ def compile_json_path(self, key_transforms, include_root=True):
                 path.append(".")
                 path.append(json.dumps(key_transform))
             else:
-                path.append("[%s]" % num)
+                if (
+                    num < 0
+                    and not self.connection.features.supports_json_negative_indexing
+                ):
+                    raise NotSupportedError(
+                        "Using negative JSON array indices is not supported on this "
+                        "database backend."
+                    )
+                path.append(self.format_json_path_numeric_index(num))
         return "".join(path)

django/db/backends/mysql/features.py

@@ -58,6 +58,8 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_stored_generated_columns = True
     supports_virtual_generated_columns = True
 
+    supports_json_negative_indexing = False
+
     @cached_property
     def minimum_database_version(self):
         if self.connection.mysql_is_mariadb:

django/db/backends/oracle/features.py

@@ -73,6 +73,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     requires_compound_order_by_subquery = True
     allows_multiple_constraints_on_same_fields = False
     supports_json_field_contains = False
+    supports_json_negative_indexing = False
     supports_collation_on_textfield = False
     test_now_utc_template = "CURRENT_TIMESTAMP AT TIME ZONE 'UTC'"
     django_test_expected_failures = {

django/db/backends/sqlite3/operations.py

@@ -441,3 +441,6 @@ def on_conflict_suffix_sql(self, fields, on_conflict, update_fields, unique_fiel
 
     def force_group_by(self):
         return ["GROUP BY TRUE"] if Database.sqlite_version_info < (3, 39) else []
+
+    def format_json_path_numeric_index(self, num):
+        return "[#%s]" % num if num < 0 else super().format_json_path_numeric_index(num)

docs/releases/6.0.txt

@@ -208,6 +208,9 @@ Models
 * :meth:`.QuerySet.raw` now supports models with a
   :class:`~django.db.models.CompositePrimaryKey`.
 
+* :class:`~django.db.models.JSONField` now supports
+  :ref:`negative array indexing <key-index-and-path-transforms>` on SQLite.
+
 Pagination
 ~~~~~~~~~~
 

docs/topics/db/queries.txt

@@ -1092,6 +1092,8 @@ Unless you are sure you wish to work with SQL ``NULL`` values, consider setting
 
 .. fieldlookup:: jsonfield.key
 
+.. _key-index-and-path-transforms:
+
 Key, index, and path transforms
 -------------------------------
 
@@ -1134,6 +1136,22 @@ array:
     >>> Dog.objects.filter(data__owner__other_pets__0__name="Fishy")
     <QuerySet [<Dog: Rufus>]>
 
+If the key is a negative integer, it cannot be used in a filter keyword
+directly, but you can still use dictionary unpacking to use it in a query:
+
+.. code-block:: pycon
+
+    >>> Dog.objects.filter(**{"data__owner__other_pets__-1__name": "Fishy"})
+    <QuerySet [<Dog: Rufus>]>
+
+.. admonition:: MySQL, MariaDB, and Oracle
+
+    Negative JSON array indices are not supported.
+
+.. versionchanged:: 6.0
+
+    SQLite support for negative JSON array indices was added.
+
 If the key you wish to query by clashes with the name of another lookup, use
 the :lookup:`contains <jsonfield.contains>` lookup instead.
 

tests/model_fields/test_jsonfield.py

@@ -785,6 +785,21 @@ def test_shallow_list_lookup(self):
             [self.objs[5]],
         )
 
+    @skipIfDBFeature("supports_json_negative_indexing")
+    def test_unsupported_negative_lookup(self):
+        msg = (
+            "Using negative JSON array indices is not supported on this database "
+            "backend."
+        )
+        with self.assertRaisesMessage(NotSupportedError, msg):
+            NullableJSONModel.objects.filter(**{"value__-2": 1}).get()
+
+    @skipUnlessDBFeature("supports_json_negative_indexing")
+    def test_shallow_list_negative_lookup(self):
+        self.assertSequenceEqual(
+            NullableJSONModel.objects.filter(**{"value__-2": 1}), [self.objs[5]]
+        )
+
     def test_shallow_obj_lookup(self):
         self.assertCountEqual(
             NullableJSONModel.objects.filter(value__a="b"),
@@ -817,12 +832,26 @@ def test_deep_lookup_array(self):
             [self.objs[5]],
         )
 
+    @skipUnlessDBFeature("supports_json_negative_indexing")
+    def test_deep_negative_lookup_array(self):
+        self.assertSequenceEqual(
+            NullableJSONModel.objects.filter(**{"value__-1__0": 2}),
+            [self.objs[5]],
+        )
+
     def test_deep_lookup_mixed(self):
         self.assertSequenceEqual(
             NullableJSONModel.objects.filter(value__d__1__f="g"),
             [self.objs[4]],
         )
 
+    @skipUnlessDBFeature("supports_json_negative_indexing")
+    def test_deep_negative_lookup_mixed(self):
+        self.assertSequenceEqual(
+            NullableJSONModel.objects.filter(**{"value__d__-1__f": "g"}),
+            [self.objs[4]],
+        )
+
     def test_deep_lookup_transform(self):
         self.assertCountEqual(
             NullableJSONModel.objects.filter(value__c__gt=2),