Rails 4:子模型可以属于两个不同的父模型吗? [英] Rails 4: can a child model belong_to two different parent models

问题描述

在我最初的Rails 4应用程序中，我具有以下模型:

In my initial Rails 4 app, I had the following models:

User
has_many :administrations
has_many :calendars, through: :administrations
has_many :comments

Calendar
has_many :administrations
has_many :users, through: :administrations
has_many :posts
has_many :comments, through: :posts

Administration
belongs_to :user
belongs_to :calendar

Post
belongs_to :calendar
has_many :comments

Comment
belongs_to :post
belongs_to :user

我刚刚向应用程序添加了新的Ad模型:

I just added a new Ad model to the app:

Ad
belongs_to :calendar

现在，我希望允许用户撰写有关广告记录的评论.

And now I would like to allow users to write comments about the ad records.

我可以使用现有的Comment模型并执行以下操作吗:

Can I use my existing Comment model and do something like:

Ad
belongs_to :calendar
has_many :comments

Comment
belongs_to :post
belongs_to :user

还是我需要创建一个独特的注释"模型，例如我将其称为AdComments或Feedback?

Or do I need to create a distinct "Comment" model, that I would call for instance AdComments or Feedback?

推荐答案

您需要使用多态关联.与此类似:

You need to use polymorphic associations. Something on the lines of this:

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end

class Ad < ActiveRecord::Base
  has_many :comments, as: :commentable
end

class Product < ActiveRecord::Base
  has_many :comments, as: :commentable
end

迁移看起来像:

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.references :commentable, polymorphic: true, index: true
      t.timestamps null: false
    end
  end
end

我猜您已经有了注释表，因此您应该使用来更改该表

I guess you already have the comments table, so you should rather change the table with

class ChangeComments < ActiveRecord::Migration
  def change
    change_table :comments do |t|
      t.rename :post_id, :commentable_id 
      t.string :commentable_type, null: false
    end
  end
end

还请注意，如果您拥有实时数据，则应将所有现有注释的commentable_type字段更新为Post.您既可以在迁移中也可以从控制台中完成.

Also beware, that if you have live data you should update the commentable_type field of all already existing comments to Post. You can either do it in a migration or from the console.

Comment.update_all commentable_type: 'Post'

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