Fix Model.save() updates and QuerySet.update() for $-prefixed strings

Author: WaVEV

django_mongodb_backend/compiler.py

@@ -883,7 +883,9 @@ def execute_sql(self, result_type):
                         f"{field.__class__.__name__}."
                     )
             prepared = field.get_db_prep_save(value, connection=self.connection)
-            if hasattr(value, "as_mql"):
+            if is_direct_value(value):
+                prepared = {"$literal": prepared} if isinstance(value, str) else prepared
+            else:
                 prepared = prepared.as_mql(self, self.connection, as_expr=True)
             values[field.column] = prepared
         try:

django_mongodb_backend/test.py

@@ -19,3 +19,18 @@ def assertAggregateQuery(self, query, expected_collection, expected_pipeline):
             eval(pipeline[:-1], {"SON": SON, "ObjectId": ObjectId, "Decimal128": Decimal128}, {}),  # noqa: S307
             expected_pipeline,
         )
+
+    def assertUpdateQuery(self, query, expected_collection, expected_condition, expected_values):
+        """
+        Assert that the logged query is equal to:
+            db.{expected_collection}.update_many({expected_condition}, {expected_values})
+        """
+        prefix, pipeline = query.split("(", 1)
+        _, collection, operator = prefix.split(".")
+        self.assertEqual(operator, "update_many")
+        self.assertEqual(collection, expected_collection)
+        condition, values = eval(  # noqa: S307
+            pipeline[:-1], {"SON": SON, "ObjectId": ObjectId, "Decimal128": Decimal128}, {}
+        )
+        self.assertEqual(condition, expected_condition)
+        self.assertEqual(values, expected_values)

tests/basic_/tests.py

@@ -14,6 +14,38 @@ def test_insert_dollar_prefix(self):
         self.assertEqual(obj.name, "$foobar")
 
 
+class UpdateDollarPrefixTests(MongoTestCaseMixin, TestCase):
+    def test_update_dollar_prefix(self):
+        """$-prefixed values are correctly saved on update."""
+        obj = Author.objects.create(name="foobar")
+        obj.name = "$updated"
+        with self.assertNumQueries(1) as ctx:
+            obj.save()
+        obj.refresh_from_db()
+        self.assertEqual(obj.name, "$updated")
+        self.assertUpdateQuery(
+            ctx.captured_queries[0]["sql"],
+            "basic__author",
+            {"_id": obj.id},
+            [{"$set": {"name": {"$literal": "$updated"}}}],
+        )
+
+    def test_update_dollar_prefix_in_value_expression(self):
+        """$-prefixed Value() expressions are correctly handled on update."""
+        obj = Author.objects.create(name="foobar")
+        obj.name = Value("$updated")
+        with self.assertNumQueries(1) as ctx:
+            obj.save()
+        obj.refresh_from_db()
+        self.assertEqual(obj.name, "$updated")
+        self.assertUpdateQuery(
+            ctx.captured_queries[0]["sql"],
+            "basic__author",
+            {"_id": obj.id},
+            [{"$set": {"name": {"$literal": "$updated"}}}],
+        )
+
+
 class QueryDollarPrefixTests(MongoTestCaseMixin, TestCase):
     def test_query_injection(self):
         """$-prefixed Value() expressions are correctly handled on update."""