Rails 4嵌套表单在编辑中显示，但不在模态中显示

# 模型定义
class Article < ActiveRecord::Base
  has_many :tags
  accepts_nested_attributes_for :tags, allow_destroy: true
end

class Tag < ActiveRecord::Base
  belongs_to :article
end

# 控制器定义
class ArticlesController < ApplicationController
  def edit
    @article = Article.find(params[:id])
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  private
    def article_params
      params.require(:article).permit(:title, :content, tags_attributes: [:id, :name, :_destroy])
    end
end

# 视图定义
<%= form_for @article do |f| %>
  <%= f.label :title %>
  <%= f.text_field :title %>

  <%= f.label :content %>
  <%= f.text_area :content %>

  <%= f.fields_for :tags do |tag_fields| %>
    <%= tag_fields.label :name %>
    <%= tag_fields.text_field :name %>
    <%= tag_fields.check_box :_destroy %>
    <%= tag_fields.label :_destroy, 'Remove' %>
  <% end %>

  <%= link_to_add_fields 'Add Tag', f, :tags %>

  <%= f.submit %>
<% end %>

# JavaScript定义
function removeFields(link) {
  $(link).prev('input[type=hidden]').val('1');
  $(link).closest('.fields').hide();
}

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

$(document).on('click', '.remove_fields', function(e) {
  e.preventDefault();
  removeFields(this);
});

$(document).on('click', '.add_fields', function(e) {
  e.preventDefault();
  var association = $(this).data('association');
  var content = $(this).data('content');
  addFields(this, association, content);
});