Rails and class variables: will this persist across users and server calls? - ruby-on-rails

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.

Answer 2

I've just came across the same issue and found this post. I know it's an old question, but posting my answer just in case someone else faces similar issue...
I think for cases where database or Rails.cache can not be used for some reason then the best place to put those values is Application class. Just define some attribute and initialize it. Then it's easy to access it just like Rails.application.heros. Quick and dirty sample below:
in config/application.rb
module YourRailsApp
class Application < Rails::Application
attr_reader :heros
initializer "init heros" do
#heros = []
hero = {}
hero['name'] = 'so'
hero['superpowers'] = ['coding', 'qa', 'spec_writing']
#heros.push hero
hero2 = {}
hero2['name'] = 'so2'
hero2['superpowers'] = ['coding']
#heros.push hero2
end
#Other application sutff...
end
end

Answer 3

I sometimes used what I called the cache of the poor.
It worked as follow:
in an initializer, add: MY_CACHE_HASH = {}
wherever you want: MY_CACHE_HASH[:foo] = :bar
wherever you need MY_CACHE_HASH[:foo] #=> :bar
I wouldn't recommend it though: what would you do if your server crashes?

Answer 4

If you have data that won't be changed while rails is running then it's fine to use a ##class_variable.
keep in mind that (in the default development configuration) controller classes are re-loaded at every request, so if you need to say, read the data from a file, consider putting the code to initialize the data into config/application.rb in a $global or CONSTANT_VAR.

Answer 5

So what you're describing is a datastructure that is not a database. I think it's perfectly reasonable to have items that "never" change in your code and not in your database.
for example, You could have:
In app/models/hero.rb
class Hero
##all_heros = []
def self.all_heros
##all_heros
end
def self.add_hero(hero)
##all_heros << hero
end
def initialize(name, superpowers=[])
#name = name
#superpowers = superpowers
end
end
# this will get executed on load
Hero.add_hero( Hero.new("so", ['coding', 'qa', 'spec_writing']))
Then later in your code, you'll access:
#heros = Hero.all_heros
And later you can swap out for a database backed store if you need on.