我遇到了一种我不太确定如何建模的情况。
编辑:下面的代码现在代表一个可行的解决方案。不过,我仍然对更好看的解决方案感兴趣。
假设我有一个 User 类,并且一个用户有很多服务。然而,这些服务是完全不同的,例如 aMailService
和 a BackupService
,所以单表继承是行不通的。相反,我正在考虑将多态关联与抽象基类一起使用:
class User < ActiveRecord::Base
has_many :services
end
class Service < ActiveRecord::Base
validates_presence_of :user_id, :implementation_id, :implementation_type
validates_uniqueness_of :user_id, :scope => :implementation_type
belongs_to :user
belongs_to :implementation, :polymorphic => true, :dependent => :destroy
delegate :common_service_method, :name, :to => :implementation
end
#Base class for service implementations
class ServiceImplementation < ActiveRecord::Base
validates_presence_of :user_id, :on => :create
#Virtual attribute, allows us to create service implementations in one step
attr_accessor :user_id
has_one :service, :as => :implementation
after_create :create_service_record
#Tell Rails this class does not use a table.
def self.abstract_class?
true
end
#Name of the service.
def name
self.class.name
end
#Returns the user this service
#implementation belongs to.
def user
unless service.nil?
service.user
else #Service not yet created
@my_user ||= User.find(user_id) rescue nil
end
end
#Sets the user this
#implementation belongs to.
def user=(usr)
@my_user = usr
user_id = usr.id
end
protected
#Sets up a service object after object creation.
def create_service_record
service = Service.new(:user_id => user_id)
service.implementation = self
service.save!
end
end
class MailService < ServiceImplementation
#validations, etc...
def common_service_method
puts "MailService implementation of common service method"
end
end
#Example usage
MailService.create(..., :user => user)
BackupService.create(...., :user => user)
user.services.each do |s|
puts "#{user.name} is using #{s.name}"
end #Daniel is using MailService, Daniel is using BackupService
请注意,我希望在创建新服务时隐式创建 Service 实例。
那么,这是最好的解决方案吗?或者甚至是一个好的?您是如何解决此类问题的?