很抱歉有一个新手问题...嵌套字段排序有问题-排序不起作用，我做错了什么？

documents.py：

class ProductDocument(Document):

name = fields.StringField(
    fields={
        'raw': fields.StringField(analyzer='keyword'),'suggest': fields.CompletionField(),}
)

brand = fields.nestedField(
    properties={
        'id': fields.IntegerField(),'name': fields.StringField(
            analyzer='keyword',fields={
                'suggest': fields.CompletionField(),}
        ),}
)

views.py：

class GetProductViewset(DocumentViewSet):

document = ProductDocument
serializer_class = GetProductSerializer`

filter_backends = [
    FilteringFilterBackend,CompoundSearchFilterBackend,SuggesterFilterBackend,OrderingFilterBackend,]
ordering_fields = {
    'name': 'name.raw','brand': {
        'field': 'brand.name','path': 'brand',},}

ordering = ('brand','name',)

提前谢谢