Oas31 validator fix

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()

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'
+    }

tests/test_regressions.py

@@ -3421,3 +3421,26 @@ class XViewSet(viewsets.ReadOnlyModelViewSet):
     schema = generate_schema('/x', XViewSet)
     assert schema['paths']['/x/']['get']["operationId"] == 'list_x'
     assert schema['paths']['/x/{id}/']['get']["operationId"] == 'retrieve_x'
+
+
+class SelfReferentialSerializer(serializers.Serializer):
+    field_int = serializers.IntegerField()
+    field_self = serializers.SerializerMethodField()
+
+    def get_field_self(self) -> "SelfReferentialSerializer":
+        return SelfReferentialSerializer()  # pragma: no cover
+
+
+def test_self_referential_serializer_method_field(no_warnings):
+    class XViewset(viewsets.ModelViewSet):
+        serializer_class = SelfReferentialSerializer
+        queryset = SimpleModel.objects.all()
+
+    schema = generate_schema('/x', XViewset)
+    assert schema['components']['schemas']['SelfReferential']['properties'] == {
+        'field_int': {'type': 'integer'},
+        'field_self': {
+            'allOf': [{'$ref': '#/components/schemas/SelfReferential'}],
+            'readOnly': True
+        }
+    }