Rails Singleton Model

create_settings.rb

class CreateSettings < ActiveRecord::Migration
  def change
    create_table :settings do |t|
      t.integer   :singleton_guard
      t.string    :setting_1
      t.integer   :setting_2
      
      t.timestamps null: false
    end

    add_index(:settings, :singleton_guard, :unique => true)
  end
end

Rails Singleton Model

Rails Singleton Model

Taken from:
http://stackoverflow.com/questions/399447/how-to-implement-a-singleton-model/12463209#12463209

settings.rb

class Settings < ActiveRecord::Base
  # The "singleton_guard" column is a unique column which must always be set to '0'
  # This ensures that only one AppSettings row is created
  validates :singleton_guard, inclusion: { in: [0] }

  def self.instance
    # there will be only one row, and its ID must be '1'
    begin
      find(1)
    rescue ActiveRecord::RecordNotFound
      # slight race condition here, but it will only happen once
      row = Settings.new
      row.singleton_guard = 0
      row.save!
      row
    end
  end

  def self.method_missing(method, *args)
    if Settings.instance.methods.include?(method)
      Settings.instance.send(method, *args)
    else
      super
    end
  end

  # Validations

end

I don't think it's a good idea to hardcode id 1 in find(1) because ids are created sequentially, probably it would be better to use first_or_create.

Now I see it was implemented for an older version of Rails, so makes sense not to use first_or_create