For my blog post, using 'accepts_nested_attributes_for' and adding fields dynamically.

application.js

function add_field(link, association, content) {
  var new_id = new Date().getTime();
  var regexp = new RegExp("new_" + association, "g")
  $(link).parent().before(content.replace(regexp, new_id));
}

function remove_field = (link) {
  $(link).siblings("input[type=hidden]").val(1);
	$(link).closest(".fieldset").hide();
}

form.html.haml

= form_for @post do |f|

  // skipped

  = f.fields_for :paragraphs do |builder|
    
    // skipped

post.rb

class Post < ActiveRecord::Base
  attr_accessible :subtitle, :title, :paragraphs_attributes
  
  has_many :paragraphs, dependent: :destroy
  
  accepts_nested_attributes_for :paragraphs, allow_destroy: true

end