Global Pagination not working on DRF Project - django

Question

I have written an API on DRF which returns a list of data based on certain conditions, but the data is very large and global pagination is not applying on it. As a result, speed slows down and therefore, data is not shown properly on a single page.
I have adding following code in settings.py file:
REST_FRAMEWORK = {
"DEFAULT_PAGINATION_CLASS": "rest_framework.pagination.PageNumberPagination",
"PAGE_SIZE": 10
}
This is my API:
class TeacherViewSet(ModelViewSet):
queryset = Teacher.objects.all()
serializer_class = serializers.TeacherSerializer
authentication_classes = [TokenAuthentication]
def list(self, request, *args, **kwargs):
response = []
for teacher in queryset:
name = Student.objects.filter(teacher=teacher).values("name")
res = {"name": name}
response.append(res)
return Response(response)
Any thing wrong I am doing?

Answer 1

Since you are overriding list method you are disabling pagination feature. Default list method looks like this:
def list(self, request, *args, **kwargs):
queryset = self.filter_queryset(self.get_queryset())
page = self.paginate_queryset(queryset)
if page is not None:
serializer = self.get_serializer(page, many=True)
return self.get_paginated_response(serializer.data)
serializer = self.get_serializer(queryset, many=True)
return Response(serializer.data)
Note paginate_queryset and get_paginated_response methods which perform pagination. So if you need to override list you should include these methods as well:
def list(self, request, *args, **kwargs):
response = []
queryset = self.filter_queryset(self.get_queryset())
queryset = self.paginate_queryset(queryset)
for teacher in queryset:
name = Student.objects.filter(teacher=teacher).values("name")
res = {"name": name}
response.append(res)
return self.get_paginated_response(response)
Not related to original question but please note that performing DB query inside a loop is considered a bad practice and could affect performance of your view.
Instead of fetching student for each teacher inside for loop consider to use prefetch_related.