Initialize constants with values from DB in Rails

Question

I have a Rails v 2.0.2 application. I'd like to initialize a constant in initializers/constants.rb and set its value from DB.

smth like this:

SESSION_DURATION = SystemDB::Configuration.get('session_duration', 0).to_i.minutes

So i've got a Configuration table in PostgreSQL with row where name = 'session_duration'. This code works fine on my local Windows PC but it fails on production server with Linux with error: `retrieve_connection': ActiveRecord::ConnectionNotEstablished (ActiveRecord::ConnectionNotEstablished)

It seems to me that at the time rails initializes the constants.rb file ActiveRecord has not been initialized yet. What can i do with it?

By The Way. I use this constant in module - so it must me initialized as soon as possible. (if i understand well)

2potatocakes · Accepted Answer · 2011-10-14 11:17:20Z

1

This probably isn't the best way to do it.. If you're wanting to set a constant from a field in a database then I'm assuming it's actually a variable and not a constant. If the value changes, your application isn't actually going to pick up the change until you restart your web server. You're probably better off making a database call instead of using a reference to SESSION_DURATION in your application.. Database calls are cheap. You may want to rethink your approach.

That said, you know your application better than I do and there may be a reason you need to do this.. If that's the case, this is a bit messy but you could always just require activerecord in your constants file and manually connect to your database first..

require "rubygems"
require "activerecord"

ActiveRecord::Base.establish_connection (
  :adapter => "mysql",
  :host => "localhost",
  :username => "user",
  :password => "password",
  :database => "some_database")

All the best ;)

answered Oct 14, 2011 at 11:17

2potatocakes

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2 Comments

Andrey Eremin Over a year ago

I need to use constants and this way will duplicate DB config which is not good, but any way, thanks.

Andrey Eremin Over a year ago

Maybe i can put CONSTANTS in other file? but i need that constants to be accessed in modules (/lib/ directory)

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