Working With Rails

You can define them as constants and place them in your environment.rb file

Example

SITE_TITLE = ‘Welcome to my website’

If you need them to be visible in views and controllers only (i.e. not in models), you could always define instance variables in your ApplicationController and load them with a before_filter. Imagine a shop site where you always need to display some kind of product list:

class ApplicationController < ActionController::Base
  before_filter :load_products

  # ... other code

  private
  def load_products
    @products = Product.find(:all)
  end
end

That’s what probably most developers would consider the Rails way …

HTH

Hi Clemens,

Won’t load_products get called every time a controller method gets called? Sound like alot of overhead. Imagine the case where what you are loading are almost never going to change.

Hi,

I like to create a module in my lib folder with all these values. I also prefer to have them defined as class/module variables rather than as constants. That way, if I need to override a value (for example, in a initializer file) I will not get a warning.

You could put a file named my_config.rb in your lib folder with the following content

module MyConfig
mattr_accessor :my_variable
my_variable=’whatever’
end

Then from any place in your code (model, view, controller, helper, lib method, whatever) you can do something like
MyConfig.my_variable

If you prefer to use constants, you can do something like

module MyConfig
MY_CONSTANT=’whatever’
end

and then use it like

MyConfig::MY_CONSTANT

Regards,
javier

You may want to check out the plugin code here:

http://github.com/ctran/application_config/tree/master

Michael:
You’re definitely right – it depends on the kind of data you’re dealing with, I was just giving an example.

The plugin that Cuong mentioned is quite nifty. Other than that, Ryan Bates shows a great example in his Railscasts’ episode #85 (http://railscasts.com/episodes/85) where he uses YAML to store the config. You might want to take a look at this option.

There is a really useful bit of code in section 61 of the Advanced Rails Recipes book. It’s called ConstantCache. I use a modified version of the code from the book in my app, but you can get it as a plugin now:

http://github.com/vigetlabs/constant_cache

In my app I have a few different Role objects, with title “Admin”, “User” etc. With this plugin I can modify my model by adding a “caches_constants” line like this:

class Role < ActiveRecord::Base
  caches_constants :key => :title
end

now when my rails app loads up, all of the different roles are loaded, and constants are added to the Role class. So in my authentication code I can refer to Role::ADMIN or Role::USER.

The instances of Role which are associated with each constant are only loaded once, when the application starts up.