Today I Learned

A Hashrocket project

Mark For Destruction

Do you have some complicated logic or criteria for deleting associated records? ActiveRecord’s #mark_for_destruction may come in handy.

Let’s say we have users who author articles. We want to delete some of the user’s articles based on some criteria — those articles that have odd ids.

> user = User.first
#=> #<User...>
> user.articles.each { |a| a.mark_for_destruction if a.id.odd? }
#=> [#<Article...>, ...]
> user.articles.find(1).marked_for_destruction?
#=> true
> user.articles.find(2).marked_for_destruction?
#=> false

We’ve marked our articles for destruction and confirmed as much with the #marked_for_destruction? method. Now, to go through with the destruction, we just have to save the parent record — the user.

> user.save
   (0.2ms)  BEGIN
  User Exists (0.8ms)  SELECT  1 AS one FROM "users" WHERE ("users"."email" = 'person1@example.com' AND "users"."id" != 1) LIMIT 1
  SQL (3.0ms)  DELETE FROM "articles" WHERE "articles"."id" = $1  [["id", 1]]
  SQL (0.2ms)  DELETE FROM "articles" WHERE "articles"."id" = $1  [["id", 3]]
   (2.1ms)  COMMIT
=> true

Note: the parent record must have autosave: true declared on the association.

class User < ActiveRecord::Base
  has_many :articles, autosave: true
end
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