How to allow registered users to enable / disable notifications for event nodes? I have an event node type. The site needs to allow registered users to enable or disable notifications for this event. So on the event page (I have several views, etc) I would like to have a button is seen by registered users.  It would be either show "Enable notifications" or "Disable notifications" based on its current value.   

Ideally this would somehow associate the user and to the event (relation?) so that I can query db for all users who have enabled notifications for this event. 

Any help or ideas on how to do this?
I would use the Flag module for this. It allows per user state toggling and integrates well with Views. 


Create a Flag called notify.
Change the text that is shown to "Enable notifications" and "Disable notifications". 
Use Rules and Views to send out your notifications. 


For extra credit create a View that shows a User all of the nodes they are receiving notifications on.