def restore_object(self, attrs, instance=None):
        #watchers is not a field from the model but can be attached in the get_queryset of the viewset.
        #If that's the case we need to remove it before calling the super method
        watcher_field = self.fields.pop("watchers", None)
        self.validate_watchers(attrs, "watchers")
        new_watcher_ids = set(attrs.pop("watchers", []))
        obj = super(WatchedResourceModelSerializer, self).restore_object(attrs, instance)

        #A partial update can exclude the watchers field or if the new instance can still not be saved
        if instance is None or len(new_watcher_ids) == 0:
            return obj

        old_watcher_ids = set(obj.get_watchers().values_list("id", flat=True))
        adding_watcher_ids = list(new_watcher_ids.difference(old_watcher_ids))
        removing_watcher_ids = list(old_watcher_ids.difference(new_watcher_ids))

        User = apps.get_model("users", "User")
        adding_users = User.objects.filter(id__in=adding_watcher_ids)
        removing_users = User.objects.filter(id__in=removing_watcher_ids)
        for user in adding_users:
            services.add_watcher(obj, user)

        for user in removing_users:
            services.remove_watcher(obj, user)

        obj.watchers = obj.get_watchers()

        return obj

    def save_watchers(self):
        new_watcher_emails = set(self._watchers)
        old_watcher_emails = set(self.object.get_watchers().values_list("email", flat=True))
        adding_watcher_emails = list(new_watcher_emails.difference(old_watcher_emails))
        removing_watcher_emails = list(old_watcher_emails.difference(new_watcher_emails))

        User = apps.get_model("users", "User")
        adding_users = User.objects.filter(email__in=adding_watcher_emails)
        removing_users = User.objects.filter(email__in=removing_watcher_emails)

        for user in adding_users:
            notifications_services.add_watcher(self.object, user)

        for user in removing_users:
            notifications_services.remove_watcher(self.object, user)

        self.object.watchers = [user.email for user in self.object.get_watchers()]

    def restore_object(self, attrs, instance=None):
        #watchers is not a field from the model but can be attached in the get_queryset of the viewset.
        #If that's the case we need to remove it before calling the super method
        watcher_field = self.fields.pop("watchers", None)
        instance = super(WatchedResourceModelSerializer, self).restore_object(attrs, instance)
        if instance is not None and self.validate_watchers(attrs, "watchers"):
            new_watcher_ids = set(attrs.get("watchers", []))
            old_watcher_ids = set(services.get_watchers(instance).values_list("id", flat=True))
            adding_watcher_ids = list(new_watcher_ids.difference(old_watcher_ids))
            removing_watcher_ids = list(old_watcher_ids.difference(new_watcher_ids))

            User = apps.get_model("users", "User")
            adding_users = User.objects.filter(id__in=adding_watcher_ids)
            removing_users = User.objects.filter(id__in=removing_watcher_ids)
            for user in adding_users:
                services.add_watcher(instance, user)

            for user in removing_users:
                services.remove_watcher(instance, user)

            instance.watchers = services.get_watchers(instance)

        return instance

 def unwatch(self, request, pk=None):
     obj = self.get_object()
     self.check_permissions(request, "unwatch", obj)
     services.remove_watcher(obj, request.user)
     return response.Ok()

 def remove_watcher(self, user):
     services.remove_watcher(self, user)