How to implement a singleton model

I have a site in rails and want to have site-wide settings. One part of my app can notify the admin by SMS if a specific event happens. This is an example of a feature that I want configurable via the site-wide settings.

So I was thinking I should have a Setting model or something. It needs to be a model because I want to be able to has_many :contacts for the SMS notification.

The problem is that there can only be one post in the database for the settings model. So I was thinking of using a Singleton model but that only prevents new object to be created right?

Would I still need to create getter and setter methods for each attribute like so:

def self.attribute=(param)
  Model.first.attribute = param
end

def self.attribute
  Model.first.attribute
end

Is it perhaps not best-practice to use Model.attribute directly but always create an instance of it and use that?

What should I do here?

Solution

I am not sure I'd waste the database/ActiveRecord/Model overhead for such a basic need. This data is relatively static (I am assuming) and on the fly calculations aren't necessary (including database lookups).

Having said that, I'd recommend you define a YAML file with your site-wide settings and define an initializer file that loads the settings into a constant. You won't have nearly as many of the unnecessary moving parts.

There is no reason that data couldn't just sit in memory and save you a ton of complexity. Constants are available everywhere, and they don't need to be initialized or instantiated. If its absolutely critical that you utilize a class as a singleton, I'd recommend doing these two things:

undef the initialize/new method
define only self.* methods that way it is not possible for you to maintain a state