Class instance variables in ActiveRecord (Ruby On Rails)

Question

I am trying to store a value in a model class, for example, values of couple of checkboxes.

I figured I could store them in a class instance variable, however, these values are cleared when I a user clicks elsewhere on the screen.

How can I maintain the values of my class instance variables.

For example

class Person < ActiveRecord::Base

   def setAge(age)
      @@age = age

   def getAge
      return @@age

however, looks like @@age is empty after it is being set.

this code is definitely not Ruby, how do we know where you're getting into trouble? — Nash Bridges, Mar 11 '12 at 15:18
@NashBridges syntactically Newton's code is valid Ruby code. Why do you think it is not? — Harish Shetty, Mar 11 '12 at 17:23
@KandadaBoggu well... even after editing it's still...Python :) — Nash Bridges, Mar 11 '12 at 17:42
The method naming conventions certainly indicates non Ruby native tongue(may be Java?). But the code will still compile and run. — Harish Shetty, Mar 11 '12 at 17:48
yes, i come from a Java background. Should I have written snake_case code for it to be more Ruby friendly? — Karan, Mar 12 '12 at 00:51
In Ruby most of the developers use snake case. Apart from that, one typically uses `attr_accessor`(http://www.rubyist.net/~slagell/ruby/accessors.html) instead of explicit getters and setters. — Harish Shetty, Mar 12 '12 at 01:00

Harish Shetty · Accepted Answer · 2012-03-11T17:49:20.517

The rails framework reloads the classes in the development mode. Any values set in prior requests to class variable is lost in a new request. If you run your server in the production mode, your code will work.

What you are trying to do is a bad practice as concurrent requests can overwrite the state and when you spawn multiple instances of your rails server this solution will not work(as mentioned by @iltempo)

If you are trying to persist the state across two client requests, you are better off using session variables.

request 1

session[:age] = params['age']

request 2

u = User.new
u.age = session[:age]

score 1 · Answer 2 · answered Mar 11 '12 at 15:31

As @nash mentioned this is not Ruby code here.

However if you store data on class level it is only valid for the current process. That means if you run multiple processes like passenger and other web servers data will not be shared between these processes.

Also age sounds to be related to a Person instance instead of the class.

Class instance variables in ActiveRecord (Ruby On Rails)

2 Answers2