What is the best way to handle constants in Ruby when using Rails?

Question

I have some constants that represent the valid options in one of my model's fields. What's the best way to handle these constants in Ruby?

Answer 1

You can use an array or hash for this purpose (in your environment.rb):

OPTIONS = ['one', 'two', 'three'] OPTIONS = {:one => 1, :two => 2, :three => 3} 

or alternatively an enumeration class, which allows you to enumerate over your constants as well as the keys used to associate them:

class Enumeration   def Enumeration.add_item(key,value)     @hash ||= {}     @hash[key]=value   end    def Enumeration.const_missing(key)     @hash[key]   end       def Enumeration.each     @hash.each {|key,value| yield(key,value)}   end    def Enumeration.values     @hash.values || []   end    def Enumeration.keys     @hash.keys || []   end    def Enumeration.[](key)     @hash[key]   end end 

which you can then derive from:

class Values < Enumeration   self.add_item(:RED, '#f00')   self.add_item(:GREEN, '#0f0')   self.add_item(:BLUE, '#00f') end 

and use like this:

Values::RED    => '#f00' Values::GREEN  => '#0f0' Values::BLUE   => '#00f'  Values.keys    => [:RED, :GREEN, :BLUE] Values.values  => ['#f00', '#0f0', '#00f']