when getting shcema, happy an exception

[fangaofeng]

Checklist

version:
django 2.2
django rest framework 3.10.3

Steps to reproduce

Example code is follow:
user Autoschema

class TrainGropMemberModifyViewSet(viewsets.ModelViewSet):
    def get_serializer_class(self):
        if self.request.method == 'PATCH':
            return TrainGropListSerializer
        if self.request.method == 'PUT':
            return TrainGroupModifySerializer

Expected behavior

get shcema

Actual behavior

File "H:\trian\whlrest\traingroup\api.py", line 34, in get_serializer_class
if self.request.method == 'PATCH':
AttributeError: 'NoneType' object has no attribute 'method'

when i use drf_yasg, drf_yasg can return correct schema.

[fangaofeng]

i think , when if public ,should give public but not reques =None.
And then check view permission,if public not check .

class SchemaGenerator(BaseSchemaGenerator):
    def get_schema(self, request=None, public=False):
        """
        Generate a OpenAPI schema.
        """
        self._initialise_endpoints()

        paths = self.get_paths(None if public else request)
        if not paths:
            return None

class BaseSchemaGenerator(object):
    def has_view_permissions(self, path, method, view):
        """
        Return `True` if the incoming request has the correct view permissions.
        """
        if view.request is None:
            return True

        try:
            view.check_permissions(view.request)
        except (exceptions.APIException, Http404, PermissionDenied):
            return False
        return True

maby change:

class SchemaGenerator(BaseSchemaGenerator):
    def get_schema(self, request=None, public=False):
        """
        Generate a OpenAPI schema.
        """
        self._initialise_endpoints()

        paths = self.get_paths(public,request)
        if not paths:
            return None

class BaseSchemaGenerator(object):
    def has_view_permissions(self,public, path, method, view):
        """
        Return `True` if the incoming request has the correct view permissions.
        """
        if public is True:
            return True

        try:
            view.check_permissions(view.request)
        except (exceptions.APIException, Http404, PermissionDenied):
            return False
        return True

[gnuletik]

I tried the following test on the master branch (commit: https://github.com/encode/django-rest-framework/tree/609f708a27bd38496b912c44742287c57e7af912):

diff --git a/tests/schemas/test_openapi.py b/tests/schemas/test_openapi.py
index 35d676d6..8dafb47e 100644
--- a/tests/schemas/test_openapi.py
+++ b/tests/schemas/test_openapi.py
@@ -1070,3 +1070,15 @@ class TestGenerator(TestCase):
         assert 'components' in schema
         assert 'schemas' in schema['components']
         assert 'Duplicate' in schema['components']['schemas']
+
+    def test_conditional_serializer(self):
+        router = routers.SimpleRouter()
+        router.register('account', views.ConditionalViewSet, basename="account")
+        urlpatterns = router.urls
+
+        generator = SchemaGenerator(patterns=urlpatterns)
+
+        request = create_request('/')
+        schema = generator.get_schema(request=request)
+
+        print(schema)
diff --git a/tests/schemas/views.py b/tests/schemas/views.py
index 1c8235b4..d3eeb6a6 100644
--- a/tests/schemas/views.py
+++ b/tests/schemas/views.py
@@ -11,7 +11,7 @@ from rest_framework.decorators import action
 from rest_framework.response import Response
 from rest_framework.schemas.openapi import AutoSchema
 from rest_framework.views import APIView
-from rest_framework.viewsets import GenericViewSet
+from rest_framework.viewsets import ModelViewSet, GenericViewSet
 
 
 class ExampleListView(APIView):
@@ -215,3 +215,11 @@ class ExampleAutoSchemaDuplicate2(generics.GenericAPIView):
 
         serializer = self.get_serializer(data=now.date(), datetime=now)
         return Response(serializer.data)
+
+
+class ConditionalViewSet(ModelViewSet):
+    def get_serializer_class(self):
+        if self.request.method == 'PATCH':
+            return ExampleSerializer
+        else:
+            return ExampleSerializerModel

I just had to change the get_serializer_class condition in order to always return a serializer and it worked.

I had the following Exception if I don't always return a serializer (which makes sense).

rest_framework/schemas/openapi.py:588: in _get_serializer
    return view.get_serializer()
rest_framework/generics.py:110: in get_serializer
    return serializer_class(*args, **kwargs)
E   TypeError: 'NoneType' object is not callable

Can give another try with the master branch and create a PR with a failing test (in case it does not work)?
Thanks!

[carltongibson]

I just had to change the get_serializer_class condition in order to always return a serializer and it worked.

That's exactly right.

Your get_serializer() needs to work without a request.

Maybe there's a docs PR for this but...