From 6a4c342e45fbd556dc1938923b7bed17031c79c7 Mon Sep 17 00:00:00 2001
From: Dmitry Voronenkov <divomen@gmail.com>
Date: Tue, 18 Jun 2019 16:13:29 +0300
Subject: [PATCH 1/2] Supported updates of an array by negative index

---
 mongoengine/base/datastructures.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mongoengine/base/datastructures.py b/mongoengine/base/datastructures.py
index fafc08b7..9307556f 100644
--- a/mongoengine/base/datastructures.py
+++ b/mongoengine/base/datastructures.py
@@ -108,6 +108,9 @@ class BaseList(list):
         super(BaseList, self).__init__(list_items)
 
     def __getitem__(self, key):
+        # change index to positive value because MongoDB does not support negative one
+        if isinstance(key, int) and key < 0:
+            key = len(self) + key
         value = super(BaseList, self).__getitem__(key)
 
         if isinstance(key, slice):

From c68e3e1238bf77997dbe65415935abe8528ffef8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastien=20G=C3=A9rard?= <bastien.gerard@cluepoints.com>
Date: Wed, 24 Jul 2019 21:37:16 +0200
Subject: [PATCH 2/2] Add test case for list update by negative index

---
 tests/document/instance.py | 49 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/tests/document/instance.py b/tests/document/instance.py
index d8841a40..d0193b60 100644
--- a/tests/document/instance.py
+++ b/tests/document/instance.py
@@ -39,10 +39,10 @@ from tests.utils import MongoDBTestCase, get_as_pymongo
 
 TEST_IMAGE_PATH = os.path.join(os.path.dirname(__file__), "../fields/mongoengine.png")
 
-__all__ = ("InstanceTest",)
+__all__ = ("TestDocumentInstance",)
 
 
-class InstanceTest(MongoDBTestCase):
+class TestDocumentInstance(MongoDBTestCase):
     def setUp(self):
         class Job(EmbeddedDocument):
             name = StringField()
@@ -3599,6 +3599,51 @@ class InstanceTest(MongoDBTestCase):
             self.assertEqual(b._instance, a)
         self.assertEqual(idx, 2)
 
+    def test_updating_listfield_manipulate_list(self):
+        class Company(Document):
+            name = StringField()
+            employees = ListField(field=DictField())
+
+        Company.drop_collection()
+
+        comp = Company(name="BigBank", employees=[{"name": "John"}])
+        comp.save()
+        comp.employees.append({"name": "Bill"})
+        comp.save()
+
+        stored_comp = get_as_pymongo(comp)
+        self.assertEqual(
+            stored_comp,
+            {
+                "_id": comp.id,
+                "employees": [{"name": "John"}, {"name": "Bill"}],
+                "name": "BigBank",
+            },
+        )
+
+        comp = comp.reload()
+        comp.employees[0]["color"] = "red"
+        comp.employees[-1]["color"] = "blue"
+        comp.employees[-1].update({"size": "xl"})
+        comp.save()
+
+        assert len(comp.employees) == 2
+        assert comp.employees[0] == {"name": "John", "color": "red"}
+        assert comp.employees[1] == {"name": "Bill", "size": "xl", "color": "blue"}
+
+        stored_comp = get_as_pymongo(comp)
+        self.assertEqual(
+            stored_comp,
+            {
+                "_id": comp.id,
+                "employees": [
+                    {"name": "John", "color": "red"},
+                    {"size": "xl", "color": "blue", "name": "Bill"},
+                ],
+                "name": "BigBank",
+            },
+        )
+
     def test_falsey_pk(self):
         """Ensure that we can create and update a document with Falsey PK."""