FormBuilder addition for models that accept nested attributes.

accept_nested_attributes.js

function addNestedRow(e) {
  e.preventDefault();

  // http://railscasts.com/episodes/197-nested-model-form-part-2
  var html = $('#my-attribute-link-template').html();
  var $attr_row = $(html.replace(/new_MyAttribute/g, new Date().getTime()));

  $('#my-attributes').append($attr_row);
};

form_builder_accept_nested_attributes.rb

class FormBuilder
  def accept_nested_attributes_for(attribute)
    attribute = attribute.to_s
    singular = attribute.singularize
    humanized = singular.underscore.humanize.titleize
    css_class = attribute.underscore.dasherize
    css_class_singular = css_class.singularize

    "".tap do |html|

      html << @template.content_tag(:div, id: css_class) do
        simple_fields_for attribute do |c|
          yield(c)
        end
      end

      html << @template.link_to("+ Add #{humanized}", '#', id: "add-#{css_class_singular}")

      html << @template.content_tag(:script, id: "#{css_class_singular}-template", type: "text/x-handlebars-template") do
        simple_fields_for attribute, singular.constantize.new, child_index: "new_#{singular}" do |c|
          yield(c)
        end
      end
    end.html_safe
  end
end