Thanks Marcio!

I found that the SetNotifications method can override other notifications set by a user for a specific piece of content, so if the user had previously turned on a different notification and we use SetNotifications in the wrong way, we can end up turning off the other notifications for that user.

I found that you can use CreateNotification instead to turn on a specific notification without affecting the others.

Ended up with something like the code below, hopefully this can help someone if they ever come across it :)

My example should turn on the Publish notification whenever a piece of content with the alias 'contentPage' is saved, so if a new contentPage is created our user will automatically have the Publish notification turned on

public class NotificationSubscribeComposer : ComponentComposer<NotificationSubscriberComponent> { }

public class NotificationSubscriberComponent : IComponent
{
    private readonly INotificationService _notificationService;
    private readonly IUserService _userService;

    public NotificationSubscriberComponent(INotificationService notificationService, IUserService userService)
    {
        _notificationService = notificationService;
        _userService = userService;
    }

    // Add event handler for when any content is saved (or saved and published)
    public void Initialize() => ContentService.Saved += ContentService_Saved;

    private void ContentService_Saved(IContentService sender, ContentSavedEventArgs e)
    {
        // We might be saving multiple pieces of content at once, so loop through them :)
        foreach (var content in e.SavedEntities)
        {
            SubscribeUser(content);
        }
    }

    private void SubscribeUser(IContent content)
    {
        // Only continue if the type of content has the alias 'contentPage'
        if (!content.ContentType.Alias.InvariantEquals("contentPage"))
        {
            return;
        }

        // Get the user or users you want here
        var user = _userService.GetUserById(-1);

        // Get the user's current notifications
        var currentNotifications = _notificationService.GetUserNotifications(user);

        // Check if a publish notification for this content already exists
        if (currentNotifications.Any(n => n.EntityId == content.Id && n.Action.Equals(ActionPublish.ActionLetter.ToString())))
        {
            return; // Don't create the notification for the user if one already exists
        }

        // Create the notification so the user receives an email any time the content is published
        _notificationService.CreateNotification(user, content, ActionPublish.ActionLetter.ToString());
    }

    public void Terminate() => ContentService.Saved -= ContentService_Saved;
}

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