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GitHub User: balexand
Same here. I'll post if I figure something out.
If you store the fields in a serialized Hash like in this episode then there's no convenient way to select/sort by these values using ActiveRecord (but you could sort them in Ruby using Enumerable#sort_by. You should check out Hstore (episode #345).
Nevermind, Rails 4 beta as of today is back to using :child_index.
In the current Rails 4 beta, the :child_index option for fields_for doesn't work. Use :index instead.
fields = f.fields_for(association, new_object, index: id) do |builder|