为什么Rails to_json有时会包含attributes、attributes_cache、changed_attributes等？

Question

我的to_json调用有时似乎包含了一些我意想不到的额外麻烦：

{"response":
  [{"attributes":
    {
        (...actual list of key:value pairs, as expected)
    },
    "json_class":"Survey",
    "attributes_cache":{}
   },
   {"changed_attributes":{"survey_source":""},
    "attributes":
    {
     (...actual list of key:value pairs, as expected)
    },
    "json_class":"Survey",
    "attributes_cache":{}}
  ],
  "status_code":"200","status_description":"OK"}

我所期待的更接近于这个：

{"response":
  [survey: {
     (...list of key:value pairs...)
   }, 
   survey: {
     (...list of key:value pairs...)
    }
  ],
  "status_code":"200","status_description":"OK"}

据我所知，显示的额外内容被AR用来跟踪脏对象的状态，但我不确定为什么它会被to_json拾取。据我所知，我的代码并没有什么花哨的功能：

RESPONSE_OK = {"status_code" => "200", "status_description" => "OK"}
@surveys = Survey.find_all_by_state("RUNNING")
response = RESPONSE_OK.merge({"response" => @surveys})
respond_to do |format|
    format.json {
        render :json => response.to_json(:methods => :intercept, :include => {:question_groups => {:include => [:questions]}})
    }
end

我不能在Rails控制台上重现它(包括一个更简单的易读性示例，但我在实际代码中得到了相同的结果)：

  ?> s = Survey.find_by_id(49)
  => #<Survey id: 49, name: "Cat?", description: "", created_at: "2010-08-29 17:50:45", updated_at: "2010-08-29 17:50:45", order: nil, entrance_logic: nil, user_id: 187, state: "RUNNING", maxresponses: 0, isrepeatable: false, reward_description: nil, compensation_amount: 0, survey_source: nil, responses_received: nil, is_profile_survey: false, hash_id: "123", survey_alias: "456", prerequisites: nil, is_web_survey: false, max_invites: 0, is_social: true>
  >> s.to_json
  => "{"survey":{"survey_source":null,"prerequisites":null,"name":"Cat?","isrepeatable":false,"maxresponses":0,"hash_id":"123","entrance_logic":null,"created_at":"2010-08-29T17:50:45Z","survey_alias":"456","updated_at":"2010-08-29T17:50:45Z","reward_description":null,"responses_received":null,"order":null,"id":49,"user_id":187,"max_invites":0,"is_web_survey":false,"is_social":true,"is_profile_survey":false,"description":"","compensation_amount":0,"state":"RUNNING"}}"
  >> s.reward_description = "100 points"
  => "100 points"
  >> s.to_json
  => "{"survey":{"survey_source":null,"prerequisites":null,"name":"Cat?","isrepeatable":false,"maxresponses":0,"hash_id":"123","entrance_logic":null,"created_at":"2010-08-29T17:50:45Z","survey_alias":"456","updated_at":"2010-08-29T17:50:45Z","reward_description":"100 points","responses_received":null,"order":null,"id":49,"user_id":187,"max_invites":0,"is_web_survey":false,"is_social":true,"is_profile_survey":false,"description":"","compensation_amount":0,"state":"RUNNING"}}"
  >> s.changed
  => ["reward_description"]
  >> s.changed_attributes
  NoMethodError: Attempt to call private method
          from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.5/lib/active_record/attribute_methods.rb:236:in `method_missing'
          from (irb):45
          from :0
  >>

感谢你的见解！我确信我可以修改我的代码以找到解决方法(如果所有其他方法都失败了，我可以手动构建传递给to_json的散列)，但如果可能的话，我想了解一下为什么会发生这种情况。

Answer 1

我只是遇到了同样的问题--经过大量的谷歌搜索，我解决了这个问题。

您已经安装了一个JSON gem (可能是另一个gem的依赖项)，这决定了您的to_json输出。

移除宝石(如果可以的话)，它会变得很好。

:)