I need to add custom file upload handler in admin add and change view (using django 3.2). And getting an error.

So far I created custom FileUploadHandler and trying to add to request in my ModelAdmin. Created class in my appadmin.py

@admin.register(MyClass)
class MyClassAdmin(ModelAdmin):
    def get_urls(self):
        urls = super().get_urls()
        custom_urls = [
            url('^my_view/$', self.create_model_view, name='my_view'),
        ]
        return custom_urls + urls

    @csrf_exempt
    def create_model_view(self, request):
        request.upload_handlers = [CustomUploadHandler(request)]
        return super().changeform_view(request)

And getting error You cannot set the upload handlers after the upload has been processed.
What am i doing wrong? Where request is started processing?