Question

我有以下两种模式：

class Project < ActiveRecord::Base
 has_one :start_date, :class_name => 'KeyDate', :dependent => :destroy
 has_one :end_date, :class_name => 'KeyDate', :dependent => :destroy

和

class KeyDate < ActiveRecord::Base
 belongs_to :project

给定数据库中与项目相关的某个关键日期：

@key_date = KeyDate.find(:first)

有没有办法反省关系以检查@key_date是否与项目相关为start_date或end_date？

Answer 1

一种很好的方法是对KeyDate类使用单表继承

class KeyDate < ActiveRecord::Base
  belongs_to :project
end

class StartDate < KeyDate
end

class EndDate < KeyDate
end

class Project < ActiveRecord::Base
  has_one :start_date, :dependent => :destroy
  has_one :end_date, :dependent => :destroy
end

class CreateKeyDatesMigration < ActiveRecord::Migration
  def up
    create_table :key_dates do |t|
      t.date :date
      t.string :type #this is the magic column that activates single table inheritance
      t.references :project
    end
  end
  …
end

这可以让你做到

@key_date = KeyDate.find(:first)
@key_date.type # => "StartDate"

Answer 2

一种干净的方式来做你想做的就是创建STI：

http://api.rubyonrails.org/classes/ActiveRecord/Base.html

参见我在这里给出的一个例子：

Rails devise add fields to registration form when having STI

Answer 3

大声思考......

class KeyDate < ActiveRecord::Base
  belongs_to :project

  def start_date?
    project.start_date == self
  end

  def end_date?
    project.start_date == self
  end

  date_type
    [:start_date, :end_date].find {|sym| send("#{sym}?") }
  end
end

说实话，我不明白为什么你需要这个。当然，你总是会对项目有所了解吗？

通过rails中两个模型之间的多个一对一关系来识别关系

3 个答案: