Ruby on rails 让Rails3jQuery自动完成显示带有特定标记的文章实例数？

我有一个具有多对多关联的Post和Tag模型：

class Post < ActiveRecord::Base
  attr_accessible :title, :content

  has_many :taggings, :dependent => :destroy
  has_many :tags, :through => :taggings
end

class Tag < ActiveRecord::Base
  has_many :taggings, :dependent => :destroy  
  has_many :posts, :through => :taggings
  has_many :subscriptions
  has_many :subscribed_users, :source => :user, :through => :subscriptions
end

class Tagging < ActiveRecord::Base
  belongs_to :post  
  belongs_to :tag
end

\u form.html.erb:

  resources :posts do
    get :autocomplete_tag_name, :on => :collection
  end

  <div class="field">
    <%= f.label :tag_names %><br />  
    <%= f.autocomplete_field :tag_names, autocomplete_tag_name_posts_path, :"data-delimiter" => ' ' %>
  </div>

（很像StackOverflow）

如果您有任何见解或示例代码，我将不胜感激

---------------------
| dr                |
---------------------
|drinks (23)        |
|drugs (4)       |
|                   |
---------------------