UIDs in Rails

has_uid.rb

module HasUid
  extend ActiveSupport::Concern

  # Skips characters that look the same, such as 0 and O
  UID_CHARS = 'abcdefghjkmnpqrstxyzACDEFGHJKLMNPQRSTXYZ2345679'.split('')

  def self.generate_uid(length)
    Array.new(length) {
      UID_CHARS[SecureRandom.random_number(UID_CHARS.size)]
    }.join
  end

  included do
    before_create :set_uid

    def set_uid
      if uid.blank?
        while uid.blank? || self.class.where(uid: uid).exists?
          self.uid = [self.class.try(:uid_prefix), HasUid.generate_uid(16)].compact.join('_')
        end
      end
      uid
    end

    def to_param
      uid
    end
  end
end

model.rb

class Model < ApplicationRecord
  def self.uid_prefix
    'mdl'
  end
  include HasUid
  
  # ...
  
end