在Ruby ActiveRecord模型中级联删除？ [英] Cascade delete in Ruby ActiveRecord models?

问题描述

我正在跟踪rubyonrails.org上的截屏视频（创建博客）。

I was following the screencast on rubyonrails.org (creating the blog).

我有以下模型：

comment.rb

comment.rb

class Comment < ActiveRecord::Base
    belongs_to :post
    validates_presence_of :body # I added this
end

post.rb

class Post < ActiveRecord::Base
    validates_presence_of :body, :title
    has_many :comments
end

模型之间的关系运行正常，除了一件事-删除帖子记录时，我希望RoR删除所有相关的注释记录。我知道ActiveRecords是独立于数据库的，因此没有内置的方法可以创建外键，关系，ON DELETE和ON UPDATE语句。因此，是否有任何方法可以做到这一点（也许RoR本身可以负责删除相关注释？）？

Relations between models work fine, except for one thing - when I delete a post record, I'd expect RoR to delete all related comment records. I understand that ActiveRecords is database independent, so there's no built-in way to create foreign key, relations, ON DELETE, ON UPDATE statements. So, is there any way to accomplish this (maybe RoR itself could take care of deleting related comments? )?

推荐答案

是。在Rails的模型关联上，可以指定：dependent 选项，该选项可以采用以下三种形式之一：

Yes. On a Rails' model association you can specify the :dependent option, which can take one of the following three forms:

• ：destroy /：destroy_all 通过调用其 destroy 方法


• ：delete /：delete_all 所有关联的对象均被立即销毁，而无需调用其：destroy 方法


• ：nullify 所有关联对象的外键均设置为 NULL 而不调用其保存回调

• :destroy/:destroy_all The associated objects are destroyed alongside this object by calling their destroy method
• :delete/:delete_all All associated objects are destroyed immediately without calling their :destroy method
• :nullify All associated objects' foreign keys are set to NULL without calling their save callbacks

如果您有：has_many X，：through => ;，则忽略：dependent 选项。 Y 关联已建立。

Note that the :dependent option is ignored if you have a :has_many X, :through => Y association set up.

因此，在您的示例中，当帖子本身被删除时，您可以选择让该帖子删除所有与其相关的评论，而不调用每个注释的 destroy 方法。看起来像这样：

So for your example you might choose to have a post delete all its associated comments when the post itself is deleted, without calling each comment's destroy method. That would look like this:

class Post < ActiveRecord::Base
  validates_presence_of :body, :title
  has_many :comments, :dependent => :delete_all
end

Rails 4的更新：

在Rails 4中，应该使用：destroy 而不是：destroy_all 。

如果使用：destroy_all ，则会出现异常：

If you use :destroy_all, you'll get the exception:

：depend选项必须是[：destroy，：delete_all，：nullify，
：restrict_with_error，：restrict_with_exception]之一

The :dependent option must be one of [:destroy, :delete_all, :nullify, :restrict_with_error, :restrict_with_exception]

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