Apply notification with more than one notification type by user preference

Thanks for the comments.

I poked at it a little with something like this but got nowhere:

apply Notification "email-service" to Service {
  vars.message_transport = {{
     var res = {}

     for (u in get_objects(User)) {
        if ( {
          res = "email"

    return res
assign where && service.vars.message_transport

Code plagarized in part from:
Execute a notificationCommand with multiple users - Icinga 2 - Icinga Community

The use case is when you have a user that has two notification methods for one service, perhaps warning goes to email and critical and unknown go to pager. The alternative is to have a group for each notification method.