In your db, chapters likely have a book_id (if you are using a SQL db). If so, your services should reflect that.
Yes, associations are a second class citizen because I've not found a comprehensive and non-leaking solution. Those circular references are dangerous (a reference to book on a chapter). REST describes no standard way to load associated data.
The attributes plugin does everything JMVC's associations plugin did.
And despite building/overseeing quite a few JMVC/can apps, I've not needed more than the attributes plugin provides.
If you need this and are willing to work on a comprehensive associations plugin, we can make it part of canjs. The best way to start is to create an issue on github describing what you would like.
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