How do I create a singleton global object in rails?

Question

I have an object that I want created once and accessible in one of my models. Where do I put him? I'm afraid if I put him in the model class file he'll get created every time I make a new instance of that model. I only want this object created once at start up. Here's the object:

require 'pubnub'     publish_key   = 'fdasfs' subscribe_key = 'sdfsdsf' secret_key    = 'fsdfsd' ssl_on        = false  pubnub_obj = Pubnub.new(publish_key,                     subscribe_key,                     secret_key,                     ssl_on) 

I use him like this in the model:

class Message < ActiveRecord::Base    def self.send_new_message_client(message)     message = { 'some_data' => message }     info = pubnub_obj.publish({                             'channel' => 'testing',                             'message' => message                           })     puts(info)   end  end 

Answer 1

In Rails, objects are recreated on each request. If this is some kind of service, it should be a singleton in the scope of a request.

Singleton objects should be created with the ruby singleton mixin:

require 'singleton'  class Pubnub   include Singleton    def initialize(publish_key, subscribe_key, secret_key, ssl_on)     # ...   end    def publish     # ...   end end 

Then you can call it with the instance method:

Pubnub.instance.publish 

This way you make sure that this object will actually be a singleton (only one instance will exist).

You can place it safely in the models directory, though I often prefer the lib directory or maybe create a new directory for services. It depends on the situation.

Hope it helps!

Answer 2

If you want only one instance in your whole application, use a singleton, otherwise use a class variable.

To use a singleton, include the Singleton mixin.

require 'singleton'  class Pubnub   include Singleton    attr_writer :publish_key, :subscribe_key, :secret_key, :ssl_on    def publish     #...   end end 

and then use it like this:

require 'pubnub'     class Message < ActiveRecord::Base   Pubnub.instance.publish_key = 'xyz'   Pubnub.instance.subscribe_key = 'xyz'   Pubnub.instance.secret_key = 'xyz'   Pubnub.instance.ssl_on = 'xyz'    def self.send_new_message_client(message)     message = { 'some_data' => message }     info = Pubnub.instance.publish({                             'channel' => 'testing',                             'message' => message                           })     puts(info)   end end 

You could also make it a class variable, to link it more tightly to a specific model:

require 'pubnub'     class Message < ActiveRecord::Base     @@pubnub_obj = Pubnub.new('xyz', 'xyz', 'xyz', 'xyz')    def self.send_new_message_client(message)     message = { 'some_data' => message }     info = @@pubnub_obj.publish({                             'channel' => 'testing',                             'message' => message                           })     puts(info)   end  end