SimpleMetadata: create schema endpoints doesn't work as expected for generic viewset with UpdateModelMixin

[timur-orudzhov]

Steps to reproduce

• Define custom schema (aka api resource meta data) as described in the docs for generic viewset with UpdateModelMixin – https://www.django-rest-framework.org/api-guide/metadata/#creating-schema-endpoints

• Check out the meta endpoint v1/api/resource_name/schema/ and that endpoint doesn't return any info about actions PUT/PATCH.

Is there way to define meta data endpoint about PUT/PATCH for the update/partial update generic viewset?

[timur-orudzhov]

I think problem is located in SimpleMetadata.determine_actions, when I use the custom schema endpoint, view.allowed_methods returns ['GET', 'HEAD', 'OPTIONS'] that, I think, is wrong cause it doesn't include, in my case, the PUT method:

    def determine_actions(self, request, view):
        """
        For generic class based views we return information about
        the fields that are accepted for 'PUT' and 'POST' methods.
        """
        actions = {}
        for method in {'PUT', 'POST'} & set(view.allowed_methods):
            view.request = clone_request(request, method)
            try:
                # Test global permissions
                if hasattr(view, 'check_permissions'):
                    view.check_permissions(view.request)
                # Test object permissions
                if method == 'PUT' and hasattr(view, 'get_object'):
                    view.get_object()
            except (exceptions.APIException, PermissionDenied, Http404):
                pass
            else:
                # If user has appropriate permissions for the view, include
                # appropriate metadata about the fields that should be supplied.
                serializer = view.get_serializer()
                actions[method] = self.get_serializer_info(serializer)
            finally:
                view.request = request

        return actions

[timur-orudzhov]

My workaround for this issue, maybe it would useful for others:

class ApiMetadata(SimpleMetadata):
    """Metadata class that supports custom schema endpoints."""

    @staticmethod
    def _determine_view_methods(view):
        """Determine http methods that viewset is supported."""
        methods = []

        if hasattr(view, 'update'):
            methods.append(HTTP_PUT_METHOD)

        if hasattr(view, 'create'):
            methods.append(HTTP_POST_METHOD)

        return methods

    def determine_actions(self, request, view):
        actions = {}
        for method in self._determine_view_methods(view):
            view.request = clone_request(request, method)
            try:
                # Test global permissions
                if hasattr(view, 'check_permissions'):
                    view.check_permissions(view.request)
            except (exceptions.APIException, PermissionDenied, Http404):
                pass
            else:
                # If user has appropriate permissions for the view, include
                # appropriate metadata about the fields that should be supplied.
                serializer = view.get_serializer()
                actions[method] = self.get_serializer_info(serializer)
            finally:
                view.request = request

        return actions

and that way we can use it:

class MetaDataViewSetMixin:
    """Metadata mixin."""

    @action(
        methods=[HTTP_GET_METHOD],
        detail=False,
        pagination_class=None,
        permission_classes=[],
    )
    def meta(self, request):
        meta = self.metadata_class()
        data = meta.determine_metadata(request, self)
        return Response(data)