accepts_nested_attributes

_option_fields.html.haml

%fieldset.answer
  = f.label :title
  = f.text_field :title
  = f.label :body
  = f.text_field :body
  = f.check_box :_destroy
  = f.label :_destroy
  %br

_form.html.haml

= form_for(@question) do |f|
  - if @question.errors.any?
    #error_explanation
      %h2
        = pluralize(@question.errors.count, "error")
        prohibited this question from being saved:
      %ul
        - @question.errors.full_messages.each do |msg|
          %li= msg
  .field
    = f.label :title
    %br
    = f.text_field :title
  .field
    = f.label :body
    %br
    = f.text_area :body
  %h3 Options
  = f.fields_for :options do |opt|
    = render "option_fields", f: opt
    
  = link_to_add_fields "Add Option", f, :options
  %br

  = f.submit

application_helper.rb

module ApplicationHelper


  def link_to_add_fields(anchor_text, form_object, association)
    new_nested_object = form_object.object.send(association).new
    id                = new_nested_object.object_id

    field_html       = form_object.fields_for(association, new_nested_object, child_index: id) do |ff|
                         render(association.to_s.singularize + "_fields", f: ff)
                       end

    link_to(anchor_text, "javascript:void(0);", class: "add_fields", 
            data: {id: id, field_html: field_html.gsub("\n", "")})
  end


end

questions.js.coffee

$(document).on "click", "form .add_fields", ->
  time  = new Date().getTime()
  regex = new RegExp($(this).data("id"), "g")
  item_fields_html = $(this).data("field-html").replace(regex, time)
  $(this).before(item_fields_html)