Add automatic token generation to a Rails model using concerns. Required a string field called token on the model.

tokenable.rb

module Tokenable
  extend ActiveSupport::Concern

  included do 
    before_validation :generate_token, unless: :persisted?, if: Proc.new { |tokenable| tokenable.token.blank? } 
  end

  protected

  def generate_token
    self.token = loop do 
      random_token = SecureRandom.urlsafe_base64(8, false)
      break random_token unless self.class.exists?(token: random_token)
    end
  end
end

tokenable_model.rb

class TokenableModel < ActiveRecord::Base
  include Tokenable

  validates :token, presence: true, uniqueness: true
end