has_many和单表继承 [英] has_many and single table inheritance

问题描述

我在两个实体Feed和Post之间具有has_many关系.我也有特定类型的帖子，视频和照片.这是在数据库中使用单表继承结构化的.

I have a has_many relationship between two entities, Feeds and Posts. I also have specific types of posts, Videos and Photos. This is structured in the database using single table inheritance.

现在，我的Feed模型指定了Feed和Post(包括子类型)之间的has_many关系

Right now I have my Feed model specifying a has_many relationship between Feeds and Posts (including the subtypes)

class Feed < ActiveRecord::Base
  has_many :posts
  has_many :photos
  has_many :videos

是否有更好，更常规的方式来指定?还是我所能得到的最简单?

Is there a better, more conventional way to specify this? Or is what I have as simple as it can get?

推荐答案

如果我对您的理解正确，那么您的帖子可以是视频或照片.正如Jaryl所说，您拥有的内容可能最容易理解/处理，但是，如果您想花哨的话，可以使用单表继承或多语言关联.

If i understand you correctly you have Posts and posts can be either video or photo. as Jaryl said what you have is probably the easiest to understand/handle however if you wanted to get fancy you could use single table inheritance or polymophic associations.

STI-示例(来自带有Rails 3rd Edition的敏捷Web开发)

STI - example (from Agile Web Development with Rails 3rd Edition)

create_table :people, :force => true do |t|
   t.string :type

   #common attributes
   t.string :name
   t.string :email

   #attributes for type=Customer
   t.decimal :balance, :precision => 10, :scale => 2

   #attributes for type=Employee
   t.integer :reports_to
   t.integer :dept

   #attributes for type=Manager
   #none
end

class Person < ActiveRecord::Base
end

class Customer < Person
end

class Employee < Person
   belongs_to :boss, :class_name => "Manager", :foreign_key => :reports_to
end

class Manager < Person
end

因此，如果您创建客户

Customer.create(:name => 'John Doe', :email => '[e-mail]', :balance => 78.29)

然后您可以通过人找到它

you can then find it via person

x = Person.find_by_name('John Doe')
x.class #=> Customer
x.email #=> [e-mail]
x.balance #=> 78.29
x.some_customer_class_method # will work because the Person.find method returned a Customer object

这样您就可以

class Post < ActiveRecord::Base
end
class Photo < Post
end
class Video < Post
end

然后可以通过Post.all找到所有这些对象，但是您将获得照片和视频对象(如果发布的不是照片或视频，则返回对象)

and then you could find them all by Post.all but you would get back Photo and Video objects (and post objects if you have posts that are not photo or video)

不要忘记数据库表中的字符串:type

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