発端

ActiveRecord で after_create 使って処理を書いてたけど、ActiveJob で実行するように変更する、という状況で、トランザクション後に処理できるよう after_commit に書き換えていた。

すると、module を分けて複数コールバックを定義していた箇所で、テストが失敗していた。debugger で見てみると、以前と逆順でコールバックが実行されているようにみえる。

調査

下記のようなコードを書いて確かめた。

$ rails new callback_order
$ cd callback_order
$ rails g model book title

class CreateBooks < ActiveRecord::Migration
  def change
    create_table :books do |t|
      t.string :title, null: false

      t.timestamps null: false
    end
  end
end

class Book < ActiveRecord::Base
  before_validation do
    puts "before_validation #1"
  end

  before_validation do
    puts "before_validation #2"
  end

  after_validation do
    puts "after_validation #1"
  end

  after_validation do
    puts "after_validation #2"
  end

  before_save do
    puts "before_save #1"
  end

  before_save do
    puts "before_save #2"
  end

  before_create do
    puts "before_create #1"
  end

  before_create do
    puts "before_create #2"
  end

  after_create do
    puts "after_create #1"
  end

  after_create do
    puts "after_create #2"
  end

  after_save do
    puts "after_save #1"
  end

  after_save do
    puts "after_save #2"
  end

  after_commit do
    puts "after_commit #1"
  end

  after_commit do
    puts "after_commit #2"
  end

  after_rollback do
    puts "after_rollback #1"
  end

  after_rollback do
    puts "after_rollback #2"
  end

  before_destroy do
    puts "before_destroy #1"
  end

  before_destroy do
    puts "before_destroy #2"
  end

  after_destroy do
    puts "after_destroy #1"
  end

  after_destroy do
    puts "after_destroy #2"
  end
end

# create and commit
$ rails runner 'Book.create(title: "Martian")'
before_validation #1
before_validation #2
after_validation #1
after_validation #2
before_save #1
before_save #2
before_create #1
before_create #2
after_create #1
after_create #2
after_save #1
after_save #2
after_commit #2
after_commit #1

# create and rollback
$ rails runner 'Book.create'
before_validation #1
before_validation #2
after_validation #1
after_validation #2
before_save #1
before_save #2
before_create #1
before_create #2
after_rollback #2
after_rollback #1
...

# create, destroy and commit
$ rails runner 'Book.create(title: "Martian").destroy'
before_validation #1
before_validation #2
after_validation #1
after_validation #2
before_save #1
before_save #2
before_create #1
before_create #2
after_create #1
after_create #2
after_save #1
after_save #2
after_commit #2
after_commit #1
before_destroy #1
before_destroy #2
after_destroy #1
after_destroy #2
after_commit #2
after_commit #1

こうしてみてみると、after_commit と after_rollback のみ、定義と逆順で実行されるようだ。

issue

issue が上がっていた。

after_commit order inconsistent with other callbacks · Issue #20911 · rails/rails

余談

ちなみに通常 after_commit を使ったテストで transactional fixture を使ってる場合は、test_after_commit gem を使う必要がある。