最近在给 iphone 做接口，用 grape，打算跟 web 项目在同一个项目目录，并打算共用 model，所以选用了 grape，但是涉及到了自定义 json 数据格式的问题，前些天有问群里的大牛们，给出的方法我都试过了，并且读了下 ruby-china 的客户端 api，见到了有类似的写法：

get do
        @topics = Topic.last_actived
          .limit(page_size)
          .includes(:user)
        present @topics, :with => APIEntities::Topic
      end

这其中用到了 APIEntities::Topic，再进入到里面看个究竟，是这样的代码：

module RubyChina
  module APIEntities
    class User < Grape::Entity
      expose :_id, :name, :login, :location, :website, :bio, :tagline, :github_url
      expose(:gravatar_hash) { |model, opts| Digest::MD5.hexdigest(model.email || "") }
      expose(:avatar_url) { |model, opts| model.avatar? ? model.avatar.url(:normal) : "" }
    end

    class Reply < Grape::Entity
      expose :_id, :body, :body_html, :message_id, :created_at, :updated_at
      expose :user, :using => APIEntities::User
    end

    class Topic < Grape::Entity
      expose :_id, :title, :body, :body_html, :created_at, :updated_at, :replied_at, :replies_count, :node_name, :node_id, :last_reply_user_login
      expose :user, :using => APIEntities::User
      # replies only exposed when a single topic is fetched
      expose :replies, :using => APIEntities::Reply, :unless => { :collection => true }
    end

    class Node < Grape::Entity
      expose :_id, :name, :topics_count, :summary, :section_id, :sort
      expose(:section_name) {|model, opts| model.section.name.to_s rescue "" }
    end
  end
end

于是乎，我就照着写了一个类似的

resource :rooms do
      get '/' do
        @rooms = Room.limit 30
        present @rooms, :with => APIEntities::Room
      end
end

以及

module APIEntities
  class Room < Grape::Entity
    expose :id, :title, :custom_num, :home_type
    expose(:address) { |model, opts| model.address_info }
    expose(:price)   { |model, opts| model.price.try(:day_price) }
    expose(:first_screen)   { |model, opts| model.first_screen(:icon) }
  end
end

然后我重启 server 访问: localhost:3000/api/v1/rooms 得到了以下数据：

[
{
home_type: "1",
id: 842,
address: "唐山市xxxxx",
custom_num: 4,
price: 100,
title: "精装单间",
first_screen: "/uploads/screenshot/photo/000/312/icon_aeb963221fb8478e75df3ef480dae4c2.gif"
},
{
id: 843,
home_type: "1",
address: "上海市松江区新桥镇",
custom_num: 4,
price: 100,
title: "精装单间",
first_screen: "/uploads/screenshot/photo/000/307/icon_e3b5c399f052afaed6a14f85eee5ce12.gif"
},
{
home_type: "公寓",
id: 858,
address: "鄂尔多斯市伊金霍洛旗乌兰木伦镇",
custom_num: 1,
price: 100,
title: "精装单间",
first_screen: "/uploads/screenshot/photo/000/000/153/icon_1.jpg"
}
]

这样的数据我基本上是我想要的，因为我都为 room 对象添加了虚拟属性，解决了子父关联关系的问题。但是我还是想加一个 status，标识返回的数据状态，类似与这样：

{"status":"OK",
   {"siteId":"siteId1","siteUrl":"www.site1.300.cn","siteName":"siteName1"},
   {"siteId":"siteId2","siteUrl":"www.site2.300.cn","siteName":"siteName2"}
}

其实就是想在现有的数据的基础上加一个 status，不知道想要得到这样的结果，利用 Grape::Entity 能否实现，昨天我看了看 api 没有找到合适的方法，如果有哪位大牛对 grape 很熟悉的话，希望大家能给个建议，谢谢。