I think it would be great to support the "<<" operator on associations since there are many situations where you just want to add an item to an association, today it is only possible to replace all the association items at once.
My first idea was to overwrite the "<<" operator in the ARes association class (is it just an Array?), track all changes made and, in the save method, make a second call to "push" the new items on the association, for instance:
PUT /post/123/comments -d comments[body]="this is a comment"
Or even add an existent item:
PUT /post/123/comments -d comments[id]=456
I'm not sure so I was wondering if you have a better solution, maybe I can borrow some ideas from AR. What do you think?