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I have a Rails 2.3.10 app that uses fields_for to include fields on a has_many association's attributes. I'm using accepts_nested_attributes_for on the the parent model and its many children are being shown in the form using:

<% form_for :map do |f| %>
...
  <% f.fields_for :markers do |marker_f| %>
    <%= marker_f.text_field :lat
    <%= marker_f.text_field :long
  <% end %>
<% end %>

The fields_for helper iterates over the child marker models and the text_field inputs are generated for each. These text fields have generated id values like:

  • map_markers_attributes_0_lat and map_markers_attributes_0_long

  • map_markers_attributes_1_lat and map_markers_attributes_1_long

  • ...

  • map_markers_attributes_5_lat and map_markers_attributes_5_long

The integer in the id is an index of the records array being iterated over. How do I access this index value for use elsewhere in my code?

For example I want to use Javascript to access the id values on these inputs. 

<% form_for :map do |f| %>
...
  <% f.fields_for :markers do |marker_f| %>
    <%= marker_f.text_field :lat
    <%= marker_f.text_field :long

    <% content_for :head do %>
      <% javascript_tag do %>
        $('<%= generate_html_id(marker_f, :lat) %>').observe_field('change');
        $('<%= generate_html_id(marker_f, :long) %>').observe_field('change');
      <% end %>
    <% end %>

  <% end %>
<% end %>

I insert some javascript into the head of the html to observe the field for any changes. I need to know the id of the field and my generate_html_id method should be able to replicate the id of the field from the marker_f builder object. However I don't know how to get the index value coming from fields_for.

It seems like there should be a fields_for_with_index method but there is not:

<% form_for :map do |f| %>
...
  <% f.fields_for_with_index :markers do |marker_f, i| %>
    <%= marker_f.text_field :lat
    <%= marker_f.text_field :long

    <% content_for :head do %>
      <% javascript_tag do %>
        $('<%= generate_html_id(marker_f, :lat, i) %>').observe_field('change');
        $('<%= generate_html_id(marker_f, :long, i) %>').observe_field('change');
      <% end %>
    <% end %>

  <% end %>
<% end %>

BTW I could create custom id values for the field but would prefer to stick to the conventions.

nutcracker
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  • Having not found any way to access the @auto_index on the fields_for iterator I've solved the immediate problem; I've just created my own index for the loop. – nutcracker Jan 26 '11 at 04:04

1 Answers1

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Alternatively you could assign a CSS class to the elements in question, then hook up your listener at dom:ready by finding all elements of this class.

jemminger
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