How do you organize the mechanism for subscribing users to events?

Question

Ruby on Rails

Suppose we have a library of books. Books are added by a kind of scanner for all public books on the Internet. There are, of course, users in this library system. Users would like to subscribe to different events, for example:
- the appearance of new books
- the appearance of comments on the book
- the addition of Vasya and Petya of their books
And notifications .. Well, for example, Seryozha wants by mail, and Lyosha - sms. OK.
To manage subscriptions, we will apparently make a table of subscribers, where the subscriber user, subscription identifier, subscription class (book, user) will be indicated.
Question: How will this all work? :) The option to hang callbacks after each book save or save comment is the dumbest yet, but also the easiest.
I watched the wisperAnd to be honest, I didn't quite get it. For example, how it stores subscriber data. In the example, I indicated that there is a table, but how to teach wisper is not clear.
Are there any gems or some examples where to see how the subscription mechanism works? And then I got a little confused and it seems obvious from the text. :)

Answer 1

Seems to understand. Wisper is what you need. It's just that in the Listener you just need to look at the table of subscribers and send out the necessary notifications.