notifications_serializers.py

class NotificationReadSerializer(ModelSerializer):
    receiver = serializers.SerializerMethodField()
    was_read = serializers.SerializerMethodField()

    class Meta:
        model = ReceiverMessage
        fields = [
            'id',
            'receiver',
            'was_read'
        ]

    def get_receiver(self, instance):
        users = []
        groups = []
        for receiver in instance.receivers.all():
            if receiver.user:
                users.append(UserParentUpdateSerializer(receiver.user).data)

            if receiver.group:
                groups.append(GroupSerializer(receiver.group).data)

        return {
            'users': users,
            'groups': groups
        }

    def get_was_read(self, instance):
        children = self.context['request'].user.children.all()
        children_ids = children.values_list('id', flat=True)
        children_group_ids = children.values_list(
                'user_groups__group__id', flat=True
        )

        receivers = instance.receivers.filter(
            Q(
                user_id__in=children_ids
            ) |
            Q(
                group_id__in=children_group_ids
            )
        )

        was_read = False

        for receiver in receivers:
            was_read = receiver.was_read

        return was_read


router.register_nested(
    r"director-messages",
    r"read",
    NotificationReadViewSet,
    parent_lookup_name='director-messages',
    base_name='read'
)