example01.rb

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable,:authentication_keys => [:login]
 
  has_one :client_user
  has_one :service_user
end

class ClientUser < ActiveRecord::Base
	belongs_to :user, :dependent => :destroy
end

class ServiceUser < ActiveRecord::Base
	belongs_to :user, :dependent => :destroy
end

example02.rb

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable,:authentication_keys => [:login]
 
   belongs_to :loginable, :polymorphic => true
end

class ClientUser < ActiveRecord::Base
	has_one :user, :as => :loginable, :dependent => :destroy
end

class ServiceUser < ActiveRecord::Base
	  has_one :user, :as => :loginable, :dependent => :destroy
end