Question

We’re on Rails 3.0.6.

Will the following code persist across page loads and users in Rails? Or does it get redefined with every request? The code lives at the top of a controller.

@@list = []

hero = {}
hero['name'] = 'so'
hero['superpowers'] = ['coding', 'qa', 'spec_writing']
@@list.push hero

hero2 = {}
hero2['name'] = 'so2'
hero2['superpowers'] = ['coding']
@@list.push hero2
... more Hashes pushed into @@list

The list only changes once a month, and we would like to efficiently and quickly make this data available to page requests. We will eventually use Rails.cache to read from the database, but we’re using the following approach for now (assuming it works).

Answer 1

In development, the default behavior is for the class to be reloaded on each request, thereby resetting your class variable. In production, however, the class is initialized once and so the class variable will persist across multiple requests and multiple sessions.

You should move to a proper caching technique as soon as you can. You cannot, obviously, persist the value beyond the reloading of the class when the application is restarted. Furthermore, if the web server is multi-threaded (as it is likely to be), it may be running multiple instances of the application on different threads which do not share the class variables, potentially creating inconsistencies between requests.