From 371c083fb0620efebf7bd0188a66486403e12ecc Mon Sep 17 00:00:00 2001
From: Stefan Budeanu <stefan.budeanu@shopify.com>
Date: Thu, 1 Dec 2016 17:39:15 -0500
Subject: Emulate db trigger behaviour for after_commit :destroy, :update

Race conditions can occur when an ActiveRecord is destroyed
twice or destroyed and updated. The callbacks should only be
triggered once, similar to a SQL database trigger.
---
 .../test/cases/transaction_callbacks_test.rb       | 45 ++++++++++++++++++++++
 1 file changed, 45 insertions(+)

(limited to 'activerecord/test/cases')

diff --git a/activerecord/test/cases/transaction_callbacks_test.rb b/activerecord/test/cases/transaction_callbacks_test.rb
index dba100f5c9..391bbe8877 100644
--- a/activerecord/test/cases/transaction_callbacks_test.rb
+++ b/activerecord/test/cases/transaction_callbacks_test.rb
@@ -449,6 +449,51 @@ class CallbacksOnMultipleActionsTest < ActiveRecord::TestCase
   end
 end
 
+class CallbacksOnDestroyUpdateActionRaceTest < ActiveRecord::TestCase
+  class TopicWithHistory < ActiveRecord::Base
+    self.table_name = :topics
+
+    def self.clear_history
+      @@history = []
+    end
+
+    def self.history
+      @@history ||= []
+    end
+  end
+
+  class TopicWithCallbacksOnDestroy < TopicWithHistory
+    after_commit(on: :destroy) { |record| record.class.history << :destroy }
+  end
+
+  class TopicWithCallbacksOnUpdate < TopicWithHistory
+    after_commit(on: :update) { |record| record.class.history << :update }
+  end
+
+  def test_trigger_once_on_multiple_deletions
+    TopicWithCallbacksOnDestroy.clear_history
+    topic = TopicWithCallbacksOnDestroy.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnDestroy.find(topic.id)
+    topic.destroy
+    topic_clone.destroy
+
+    assert_equal [:destroy], TopicWithCallbacksOnDestroy.history
+  end
+
+  def test_trigger_on_update_where_row_was_deleted
+    TopicWithCallbacksOnUpdate.clear_history
+    topic = TopicWithCallbacksOnUpdate.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnUpdate.find(topic.id)
+    topic.destroy
+    topic_clone.author_name = "Test Author"
+    topic_clone.save
+
+    assert_equal [], TopicWithCallbacksOnUpdate.history
+  end
+end
+
 class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
   class TopicWithoutTransactionalEnrollmentCallbacks < ActiveRecord::Base
     self.table_name = :topics
-- 
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