blocks|key|3259136|text|简单的答案是没有。每个请求都被视为一个独立的事件，除了存储在用户会话和任何外部数据库、缓存或文件存储中的信息外，不会传递任何状态信息。最好在设计应用程序时牢记这一点，不要仅仅因为设置了它们就期望它们能够持久存在。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3259137|更复杂的情况是，有些事情确实存在。例如，您可以在控制器上创建一个类变量，正如您所期望的那样，它将从一个请求传递到下一个请求。问题是，这只适用于包含在该进程中的控制器的单个实例，而不适用于由其他进程服务的请求。如果您需要缓存，请利用Rails.cache基础设施，并避免在您自己的基础设施中进行黑客攻击。|3259138|典型的生产环境是一个复杂的、不断变化的环境，其中流程不断地被创建和销毁，并且没有办法预先确定哪个流程最终将服务于特定的请求。由于许多部署不仅涉及单个机器上的多个进程，而且还涉及多个机器，因此确实没有实际的方法来创建应用程序范围的单例对象。|3259139|您可以做的最好的事情是在缓存引擎之上构建一个层，其中您的单例对象仅仅是从缓存获取和写入的函数的包装器。这为您提供了单例对象的外观，同时保持了进程间的一致性。|3259140|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

The simple answer is none. Each request is treated as an independent event and no state information is carried over apart from what is stored in the user session and any external databases, caches, or file stores. It is best that you design your application with this in mind and not expect things to persist just because you've set them.

The more complicated story is that some things do persist. For example, you can create a class variable on a controller and this will be carried from one request to the next as you might expect. The catch is that this only applies to the singular instance of that controller, as contained within that process, and will not apply to requests served by other processes. If you need caching, make use of the Rails.cache infrastructure and avoid hacking in your own.

A typical production environment is a complicated, ever-changing thing, where processes are created and destroyed constantly and there is no way to determine in advance which process will ultimately end up serving a particular request. As many deployments involve not only multiple processes on a single machine, but multiple machines, there really is no practical way to create application-wide singleton objects.

The best thing you can do is build a layer on top of the caching engine where your singleton object is merely a wrapper to functions that fetch and write from the cache. This gives you the appearance of a singleton object while maintaining inter-process consistency.

blocks|key|3045277|text|网络是一种无状态的媒介。除非您故意在会话中保存数据，或者在get或post中传递数据，否则每个web请求都会以空白板开始。将页面传送到web浏览器后，使用当前请求创建的任何对象都会被销毁。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3045278|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The web is a stateless medium. Unless you purposely save data in a session or pass it in a get or post, each web request starts with a blank slate. Any objects created with the current request are destroyed once the page is delivered to the web browser.

blocks|key|3259210|text|我知道这篇文章很老了，但是对于正在寻找解决方案的人来说，可以使用Rails.Cache，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3259211|class+TestEventsController+<+ApplicationController
++require+'httparty'

++@@cache+=+ActiveSupport::Cache::MemoryStore.new(expires_in:+5.minutes)

++before_action+:get_data,+only:+[:get]
++before_action+:get_response,+only:+[:set]

++def+get
++++uri+=+"https://hooks.zapier.com/hooks/catch/zap_id/"
++++event_id+=+event_id_generate()
++++@@cache.write(event_id,+"")

++++result+=+HTTParty.post(uri.to_str,
++++:body+=>+{id:+event_id,+data:+@data}.to_json,
++++:headers+=>+{'content-Type'+=>+'application/json'})
++++sleep+2
++++render+json:+{+'value':+@@cache.read(event_id)+},+status:+200
++end

++def+set
++++@@cache.write(@id,+@value)
++++render+json:+{+'value':+@@cache.read(@id)+},+status:+200
++end

++def+get_data
++++@data+=+params["data"]
++end
++def+get_response
++++@id+=+params["id"]
++++@value+=+params["value"]
++end

++def+event_id_generate
++++token+=+SecureRandom.urlsafe_base64(10,+false)
++end
end|code-block|syntax|javascript|3259212|我正在做的是在一个路由上接收一个请求，向Zapier发送一个GET，然后在另一个路由上等待答案。Rails为每个请求打开一个新的Thread，所以我在RAM中以'key:+value‘格式写入数据|3259213|Rails.cache+in+different+threads+not+caching?|offset|length|3259214|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/33703928/rails-cache-in-different-threads-not-caching^0|0|0|0|0|19|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@$K|Y|L|Z|1|10]]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

I know that this post is old, but for who is looking a solution, it's possible to use Rails.Cache, like this:

<pre><code>class TestEventsController &lt; ApplicationController
 require 'httparty'

 @@cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)

 before_action :get_data, only: [:get]
 before_action :get_response, only: [:set]

 def get
 uri = "https://hooks.zapier.com/hooks/catch/zap_id/"
 event_id = event_id_generate()
 @@cache.write(event_id, "")

 result = HTTParty.post(uri.to_str,
 :body =&gt; {id: event_id, data: @data}.to_json,
 :headers =&gt; {'content-Type' =&gt; 'application/json'})
 sleep 2
 render json: { 'value': @@cache.read(event_id) }, status: 200
 end

 def set
 @@cache.write(@id, @value)
 render json: { 'value': @@cache.read(@id) }, status: 200
 end

 def get_data
 @data = params["data"]
 end
 def get_response
 @id = params["id"]
 @value = params["value"]
 end

 def event_id_generate
 token = SecureRandom.urlsafe_base64(10, false)
 end
end
</code></pre>

What I'm doing is receive a request in a route, sending a GET to Zapier, and waiting for the answer in another route. Rails opens a new Thread for each request, so I write in the RAM my data in format 'key: value'

<a href="https://stackoverflow.com/questions/33703928/rails-cache-in-different-threads-not-caching">Rails.cache in different threads not caching?</a>

I decided to use the singleton design pattern while creating a view helper class. This got me thinking; will the singleton instance survive across requests? This led to another question, Which variables (if any) survive across web requests and does that change depending on deployment? (Fastcgi, Mongrel, Passenger, ...)

I know that Controller instance variables aren't persisted. I know Constants are persisted (or reloaded?). But I don't know about class variables, instance variables on a class, Eigenclasses, ...

What data (if any) persists across web-requests in Ruby on Rails?

文件存储

数据库

路由

在创建视图助手类时，我决定使用singleton设计模式。这让我思考:单例实例会跨请求存活吗？这引出了另一个问题，哪些变量(如果有的话)在web请求中存在，这是否会随着部署的不同而变化？(Fastcgi，Mongrel，Passenger，...)我知道控制器实例变量不是持久化的。我知道常量是持久化的(或者重新加载？)...

问在Ruby on Rails中，哪些数据(如果有的话)跨web请求持久存在？
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