定义抽象类，实现代码重构

gistfile1.rb

# app/models/abstract_server.rb
class AbstractServer < ActiveRecord::Base
  self.abstract_class = true
  
  validates_presence_of :name, :address, :username, :password, :encoding
  
  validates_length_of :name, :maximum => 20, :allow_blank => true
  validates_length_of :address, :maximum => 20, :allow_blank => true
  validates_length_of :username, :password, :maximum => 20, :allow_blank => true
  validates_length_of :encoding, :maximum => 10, :allow_blank => true
end

# app/models/server.rb
class Server < AbstractServer
  # some other method
end

# app/models/sourcer.rb
class Sourcer < AbstractServer
  # some other method
end