Nested form helper based on http://transfs.com/devblog/2009/06/26/nested-forms-with-rails-2-3-helpers-and-javascript-tricks, but with Haml and jQuery

_asset.html.haml

-# Don't display new assets on form redisplay
- unless (form.object.new_record? && form.object.data.dirty?)
  %li
    = form.object.name if form.object.data?
    = form.file_field :data if form.object.new_record?
    = form.text_field :title
    = remove_link(form, t('assets.actions.remove')).html_safe!

form.html.haml

- semantic_form_for @question, :html => { :multipart => true } do |f|
  = f.input :body

  - f.inputs :name => t("models.assets"), :id => "assets" do
    - f.semantic_fields_for :assets do |asset_form|
      = f.error_message_on :assets
      = render :partial => "assets/asset", :locals => { :form => asset_form }
    %li= link_to_new_nested_form t("assets.actions.add"), f, :assets, :partial => "assets/asset"


  - f.buttons do
    = f.commit_button

nested_forms.js

// Nested forms remove link handler
$('.remove').live('click', function() {
    var link = $(this);
    if(link.hasClass('remove_new')) {
        link.parents('li').remove();
    } else {
        link.prev('input[type=hidden]').val("1");
        link.parents('li').hide();
    }
});

nested_forms_helper.rb

module NestedFormsHelper
  def remove_link(fields, name="remove")
    out = ''
    html_class = 'remove '

    if fields.object.new_record?
      html_class += "remove_new"
    else
      html_class += "remove_existing"
      out << fields.hidden_field(:_delete)
    end

    out << link_to(name, "##{fields.object.class.name.underscore}", :class => html_class)
    out
  end

  def generate_html(form_builder, method, options = {})
    options[:object]  ||= form_builder.object.class.reflect_on_association(method).klass.new
    options[:partial] ||= method.to_s.singularize
    options[:form_builder_local] ||= :form

    form_builder.fields_for(method, options[:object], :child_index => 'NEW_RECORD') do |f|
      render(:partial => options[:partial], :locals => { options[:form_builder_local] => f })
    end
  end

  def link_to_new_nested_form(name, form_builder, method, options = {})
    options[:object]             ||= form_builder.object.class.reflect_on_association(method).klass.new
    options[:partial]            ||= method.to_s.singularize
    options[:form_builder_local] ||= :form
    options[:element_id]         ||= method.to_s

    link_to_function name do |page|
      html = generate_html(
      form_builder,
      method,
      :object => options[:object],
      :partial => options[:partial],
      :form_builder_local => options[:form_builder_local]
      )

      page << %{
         $('##{options[:element_id]} ol li:last-child').before("#{ escape_javascript html }".replace(/NEW_RECORD/g, new Date().getTime()));
      }
    end
  end
end