jQuery TokenInput plugin with deep nested_attributes pre-populating tokens on edit - ruby-on-rails-3

Question

I have the following structure working on my application.
class Foo < ActiveRecord::Base
has_many :examples, :dependent => :destroy
accepts_nested_attributes_for :examples
end
class Example < ActiveRecord::Base
belongs_to :foo
has_many :codes, :dependent => :destroy
accepts_nested_attributes_for :codes, :reject_if => lambda { |a| a[:code].blank? }
end
class Code < ActiveRecord::Base
belongs_to :example
has_many :code_kinds
has_many :kinds, :through => :code_kinds
attr_reader :kind_tokens
def kind_tokens=(ids)
self.kind_ids = ids.split(",")
end
end
class CodeKind < ActiveRecord::Base
belongs_to :code
belongs_to :kind
end
class Kind < ActiveRecord::Base
has_many :code_kinds
has_many :codes, :through => :code_kinds
end
And it's working perfectly for the form with fields_for on create and save.
I'm using kind_tokens as described on RailsCast #258 Token Fields
But on the edit form everything displays perfectly now I should be pre-populating the data in a data-pre attribute on the kind_tokens field inside the nested attributes for code in examples.
The RailsCast say:
<%= f.text_field :author_tokens, "data-pre" => #book.authors.map(&:attributes).to_json %>
But I can't do #foo.examples.codes.kinds.map... because the relation with Foo and examples returns a collection, the same situation with codes.
I'm just using:
<%= f.fields_for :codes do |codes_form| %>
That's inside of
<%= f.fields_for :examples do |examples_form| %>
Now how can I pre-populate the kind for code if I don't have any loop, and everything's done by nested_attributes and fields_for ?

Answer 1

Solved
Everytime you use a
<%= f.fields_for ...
Rails automatically makes a loop so you can have some kind of counter there like:
<%
#ctrEx = 0
#ctrCd = 0
%>
<%= form_for #foo ...
<%= f.fields_for :examples do |examples_form| %>
...
<%= examples_form.fields_for :codes do |codes_form| %>
...
<%= codes_form.text_field :kind_tokens, :class => "tag_matcher", "data-pre" => #foo.examples[#ctrEx].codes[#ctrCd].kinds.map(&:attributes).to_json %>
...
<%#ctrCd +=1%>
<%end%>
...
<%
#ctrEx += 1
#ctrCd = 0
%>
<%end%>
<%end%>
Now you can use your counters in the data-pre like this:
#foo.examples[#ctrEx].codes[#ctrCd].kinds.map(&:attributes).to_json
That's the way i figured it out, but there must be another way.