Rails - May 2006 - Seeking complete example/plugin of simple usage of Lookup (auto_complete) for making associations on models

I think the second most useful usage of the auto_complete is for editing
relations (associations).

I''ve searched for almost a week on all RoR resources but I
didn''t found any solution to this problem. Instead I''ve
discovered that there are many looking for this.

I think that this problem must be clearly solved and the clear how-to should
published on one-more RoR sites.

Because I trust the power of examples I''ll try to explain the problem
using an example.

The description of the problem
------------------------------
1. We have two models: Book(s) and Contact(s). A book has_one :contact. Contact
doesn''t know about book.
2. Because we have a lots of Contacts we can''t use dropdown for
selecting a contact for a book.
3. Also because contacts can have the same name we must submit the ID of the
contact.
4. Are interested in a magic way of mapping the relations on submit. We
don''t want to write more code for every new editable relation.
5. Additional optional behavior: require a valid lookup value (empty not
accepted).

Ideas for implementation 
-------------------------
The form should submit something like this: :book => { :name => "my
book", :author => { :id => 123, :name => "John"} }

The new (improved) update_attributes should work recursively: when he will find
the :author key in the has it will know that :author is a relation and will call
update attributes for it.

I looking for comments, hints or ever portions of code related to this subject. 

PS. How do I make the Contact auto_complete to work in the book form without
inserting other instance variable?