From 32cb1fe1c66645671681407d47e8370b4afbfc3f Mon Sep 17 00:00:00 2001
From: Tim Graham <timograham@gmail.com>
Date: Thu, 30 Jul 2020 00:38:02 -0400
Subject: [PATCH] [3.1.x] Refs #31829 -- Added
 DatabaseFeatures.json_key_contains_list_matching_requires_list.

CockroachDB's behavior matches PostgreSQL.
Backport of 184a6eebb0ef56d5f1b1315a8e666830e37f3f81 from master
---
 django/db/backends/base/features.py       | 3 +++
 django/db/backends/postgresql/features.py | 1 +
 tests/model_fields/test_jsonfield.py      | 5 +++--
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 5a27aa9f17..be949423b0 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -314,6 +314,9 @@ class BaseDatabaseFeatures:
     # Does the backend support __contains and __contained_by lookups for
     # a JSONField?
     supports_json_field_contains = True
+    # Does value__d__contains={'f': 'g'} (without a list around the dict) match
+    # {'d': [{'f': 'g'}]}?
+    json_key_contains_list_matching_requires_list = False
 
     def __init__(self, connection):
         self.connection = connection
diff --git a/django/db/backends/postgresql/features.py b/django/db/backends/postgresql/features.py
index a9b9ca578a..58a84a6c33 100644
--- a/django/db/backends/postgresql/features.py
+++ b/django/db/backends/postgresql/features.py
@@ -59,6 +59,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     validates_explain_options = False  # A query will error on invalid options.
     supports_deferrable_unique_constraints = True
     has_json_operators = True
+    json_key_contains_list_matching_requires_list = True
 
     @cached_property
     def is_postgresql_9_6(self):
diff --git a/tests/model_fields/test_jsonfield.py b/tests/model_fields/test_jsonfield.py
index fa6e9e2a34..26643adcdd 100644
--- a/tests/model_fields/test_jsonfield.py
+++ b/tests/model_fields/test_jsonfield.py
@@ -699,8 +699,9 @@ class TestQuerying(TestCase):
                 )),
             ),
         ]
-        # PostgreSQL requires a layer of nesting.
-        if connection.vendor != 'postgresql':
+        # For databases where {'f': 'g'} (without surrounding []) matches
+        # [{'f': 'g'}].
+        if not connection.features.json_key_contains_list_matching_requires_list:
             tests.append(('value__d__contains', {'f': 'g'}))
         for lookup, value in tests:
             with self.subTest(lookup=lookup, value=value):