function remove_fields(link) {
    $(link).prev("input[type=hidden]").val("1");
    $(link).closest(".fields").hide();
  }

  function add_fields(link, association, content) {
    var new_id = new Date().getTime();
    var regexp = new RegExp("new_" + association, "g")
    $(link).parents('.control-group').before(content.replace(regexp, new_id));
  }