From 8156c0bef161c44e4451be3ffd22fe0266d26a50 Mon Sep 17 00:00:00 2001
From: "T. Franzel" <tfranzel@users.noreply.github.com>
Date: Tue, 1 Oct 2024 23:51:22 +0200
Subject: [PATCH] fix OAS3.1 validator omission #1302

---
 drf_spectacular/openapi.py |  4 ++++
 tests/test_oas31.py        | 23 ++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drf_spectacular/openapi.py b/drf_spectacular/openapi.py
index 12d6f274..ff0e5e36 100644
--- a/drf_spectacular/openapi.py
+++ b/drf_spectacular/openapi.py
@@ -1069,6 +1069,10 @@ def _map_basic_serializer(self, serializer, direction):
     def _insert_field_validators(self, field, schema):
         schema_type = schema.get('type')
 
+        # OAS 3.1 special case - extract the main type
+        if isinstance(schema_type, list):
+            schema_type = [t for t in schema_type if t != 'null'][0]
+
         def update_constraint(schema, key, function, value, *, exclusive=False):
             if callable(value):
                 value = value()
diff --git a/tests/test_oas31.py b/tests/test_oas31.py
index 9cdaa4cd..83ff6f9a 100644
--- a/tests/test_oas31.py
+++ b/tests/test_oas31.py
@@ -1,10 +1,11 @@
 from unittest import mock
 
-from rest_framework import serializers
+from rest_framework import serializers, viewsets
 from rest_framework.views import APIView
 
 from drf_spectacular.utils import extend_schema
 from tests import generate_schema
+from tests.models import SimpleModel
 
 
 @mock.patch('drf_spectacular.settings.spectacular_settings.OAS_VERSION', '3.1.0')
@@ -68,3 +69,23 @@ def get(self, request):
         'required': ['foo'],
         'type': 'object'
     }
+
+
+@mock.patch('drf_spectacular.settings.spectacular_settings.OAS_VERSION', '3.1.0')
+def test_validator_addition_for_oas31(no_warnings):
+
+    class XSerializer(serializers.Serializer):
+        field = serializers.CharField(allow_blank=True, allow_null=True, max_length=40, required=False)
+
+    class XViewset(viewsets.ModelViewSet):
+        serializer_class = XSerializer
+        queryset = SimpleModel.objects.none()
+
+    schema = generate_schema('x', XViewset)
+
+    assert schema['components']['schemas']['X'] == {
+        'properties': {
+            'field': {'maxLength': 40, 'type': ['string', 'null']}
+        },
+        'type': 'object'
+    }