has_sequence_id.rb

module SequenceId
  extend ActiveSupport::Concern
  module ClassMethods
    def has_sequence_id(column: "hex_id", sufix: "DBA", rjust_lenght: 3)
      after_create do
        number = self.id.to_s(16).rjust(rjust_lenght, "0")
        self.send("#{column}=", "#{sufix}_#{number}")
        self.save
      end
    end
  end
end

class User < ActiveRecord::Base
  has_sequence_id
end

user = User.create
user.hex_id #=> "DBA_0c8"

class UsersController < ActionController::Base
  def show
    @user = User.find_by_hex_id(params[:id])
  end
end