stampable.rb

module Contactable
  def self.set_contact(contact)
    @contact = Contact.find_by_email(contact[:email])
    @contact = Contact.create!(contact) unless @contact.exists?
  end
  def self.get_contact
    @contact
  end
end

module Stampable
  include Contactable

  def self.included(base)
    has_one       :stamp, as: :stampable
    after_create  :create_stamp
  end
  
  def self.create_stamp(stamp)
    self.destroy unless not @contact.nil? and @contact.valid?

    stamp = Stamp.new(stamp)
    stamp.contact = get_contact
    stamp.stampable_id = self.id
    stamp.stampable_type = self.class.table_name

    self.destroy if not stamp.save

    self.stamp = stamp
    self.save
  end
end

user.rb

class User < ActiveRecord::Base
  include Stampable
  validates :user_type,:locality,:city,       presence:   true
  validates :username,                        uniquiness: true
  
  has_secure_password
  validates_presence_of :password, :on => :create

  belongs_to  :parent,    class_name: 'User'
  has_many    :children,  class_name: 'User', foreign_key: 'parent_id'
  
  has_many    :stamps

  before_create   :generate_access_token, :set_username_as_email

private
  
  def generate_access_token
    access_token = SecureRandom.hex
    until User.find_by_access_token(access_token) == nil
      access_token = SecureRandom.hex
    end
    self.access_token = access_token
  end

  def set_username_as_email
    self.username = get_contact.email
  end
end

user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase
  test 'create user and try to save' do
    u = User.new :user_type => 'admin', :locality => 'goregaon', :city => 'mumbai'
    u.set_contact({first_name: 'Admin', last_name: 'admin', email: 'admin@example.com', contact_numbers: '1,2'})

    assert u.save
  end
end