# Managing "application scope" data - best practices **URL:** \ **Category:** Rails\ **Created:** [April 12, 2006, 1:10am UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850 "2006-04-12T01:10:08Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [April 12, 2006, 1:10am UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850/1 "2006-04-12T01:10:08Z")
All, I have some data that I need to be able to see across the application. For J2EE people out there, I need something that I want to have available in the “application scope” of my app. What is the best way to handle this? I’m trying to access a class variable that I created in my controller from my view (to no avail). Create a class variable in my helper class and use that? How do you reference a class variable from an object of another class? Thanks, Wes ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [April 12, 2006, 1:21am UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850/2 "2006-04-12T01:21:07Z")
Hi, Wes. What exactly are you trying to do? Basically speaking, Helpers are the thing you want to use if you want to share functionality across views. If you want to share a class variable (e.g. a “public static foo” in Java) across the application, then you can simply declare it the following way (includes a class method that returns an arbitrary value): class MyFoo FOO\_BAR = ‘BAZ!’ def self.bar return “BAZ AGAIN!” end end Place this in a file called “my\_foo.rb” and you should be able to access it by calling “MyFoo.bar” or “MyFoo::FOO\_BAR” anywhere in your application (Rails will load the MyFoo class automatically). \*m ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [April 12, 2006, 3:26am UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850/3 "2006-04-12T03:26:10Z")
I had a similar question about some kind of Application object, like in asp. So maybe this thread would help you [http://www.ruby-forum.com/topic/61808](http://www.ruby-forum.com/topic/61808) Saludos Sas ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [April 12, 2006, 1:51am UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850/4 "2006-04-12T01:51:36Z")
On 4/11/06, Manuel H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > class MyFoo > > \*m Does that really work? I thought each instance of ruby had its own collection of variables, so the above would fail if you ever modify the variable. I think you need to get the variable into a shared memory/db/memcache etc. for it to work the way you would expect. Personally I use session variables, but not any application wide vars. ## Greg Greg F. The Norcross Group Forensics for the 21st Century ---
**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\ **Post date:** [April 12, 2006, 6:16pm UTC](https://www.ruby-forum.com/t/managing-application-scope-data-best-practices/93850/5 "2006-04-12T18:16:38Z")
On Apr 11, 2006, at 4:10 PM, Wes G. wrote: > Create a class variable in my helper class and use that? > > How do you reference a class variable from an object of another class? > > Thanks, > Wes Wes- ``` I posted this as a tip a few days ago but no-one seemed to notice ``` it. The follwing is a nice way to get application wide context hashes or even custom classes. Hope it helps you. -Ezra -----Easy AppServer---------------- ``` An easy way to get yourself an application wide context is to use ``` drb. Ara Howard has written an awesome library called slave that takes care of forking a child process to run your drb server in and then doing a heartbeat back and forth from your rails app to the application wide classes(AppServer from here on out.). This heartbeat is needed so that when rails starts, the AppServer starts and when rails stops the AppServer stops because the heartbeat doesn’t respond anymore. ``` This slave library allows you to publish whatever class you want as ``` an application wide class. This means that all your requests can get the same application wide vars or objects no matter how many fcgi’s or mongrel’s you have serving up requests. You could also just as easily serve up an app wide array or hash. Lets look at a small example of this. ``` Get the slave library here: ``` [http://codeforpeople.com/lib/ruby/slave/slave-0.0.0/README](http://codeforpeople.com/lib/ruby/slave/slave-0.0.0/README) [http://codeforpeople.com/lib/ruby/slave/slave-0.0.0.tgz](http://codeforpeople.com/lib/ruby/slave/slave-0.0.0.tgz) ``` Now lets publish a simple hash that we can use application wide. Put ``` the following in your environment.rb file so it starts up when rails starts up. $application\_wide\_hash = Slave.new(Hash.new).object ``` Thats all. Now you can use $application_wide_hash anywhere in your ``` rails apps and it will behave just like a hash. So you are still responsible for making suitable hash keys that you can use between requests and still distinguish from one another. But since you can store any object in a ruby hash you can store anything you want in this $application\_wide\_hash. Just make a unique key and store it in the users session. Maybe something like this: ``` key = "#{current_user.id}-#{Time.now}-#{rand} session[:app_server_key] = key $application_wide_hash[key] = ``` SomeObjectOrValueYouWantToStoreInApplicationWideStorage ``` Then on the next request you can get that object back with this: $application_wide_hash[session[:app_server_key]] This approach allows for a very flexible application wide context. ``` It’s uses are only limited to your creativity 😉 Of course you might want to publish a different class then a hash in this AppServer. If you want to do that then just replace this: $application\_wide\_hash = Slave.new(Hash.new).object with this: $application\_wide\_hash = Slave.new(MyAppServerObject.new).object ``` The slave library will take care of forking a background process and ``` starting a drb server inside said process. Then the heartbeat takes care of shutting down the AppServer when you shut down rails so you don’t get orphaned AppServers. Of course all the context in your $application\_wide\_hash will be lost when you restart or shutdown rails and you are responsible for deleting things out of the $application\_wide\_hash when you are done with them. ``` If you really want the $application_wide_hash to be persistent ``` between restarts of rails then you will need to do a little custom coding yourself. With a bit of hacking you can hook into the heartbeat code and marshall the $application\_wide\_hash to disk as Yaml or binary and then reload that when rails starts back up. ``` The objects or classes that you put in the AppServer cannot contain ``` procs, lambdas or anything else that cannot be marshalled by ruby and drb. The way around this is to use DrbUndumped. I won’t go into detail about that here but you can look up resources on how to do this with google 😉 ``` I have a full chapter on this technique in my forthcoming book that ``` goes into detail of what this process can be used for and what is shouldn’t be used for. As well as concrete examples and code that folks might find useful if they need to do this kind of thing. Cheers- -Ezra