自Rails 4.2以来，外键支持显示，自动将add_foreign_key添加到迁移文件。
但是使用MySql，在销毁父对象时，会发生以下错误。
user.destroy
(0.2ms) BEGIN
Authentication Load (0.5ms) SELECT `authentications`.* FROM `authentications` WHERE `authentications`.`user_id` = 5
SQL (2.3ms) DELETE FROM `authentications` WHERE `authentications`.`id` = 4
Twitter Load (3.2ms) SELECT `twitters`.* FROM `twitters` WHERE `twitters`.`id` = 3 LIMIT 1
SQL (1.7ms) DELETE FROM `twitters` WHERE `twitters`.`id` = 3
Follow Load (0.3ms) SELECT `follows`.* FROM `follows` WHERE `follows`.`user_id` = 5
Activity Load (0.4ms) SELECT `activities`.* FROM `activities` WHERE `activities`.`trackable_id` = 16 AND `activities`.`trackable_type` = 'Follow' LIMIT 1
Feed Load (1.0ms) SELECT `feeds`.* FROM `feeds` WHERE `feeds`.`activity_id` = 40
Notification Load (0.4ms) SELECT `notifications`.* FROM `notifications` WHERE `notifications`.`activity_id` = 40
SQL (0.3ms) DELETE FROM `notifications` WHERE `notifications`.`id` = 24
SQL (1.8ms) DELETE FROM `activities` WHERE `activities`.`id` = 40
SQL (0.7ms) DELETE FROM `follows` WHERE `follows`.`id` = 16
Follow Load (0.4ms) SELECT `follows`.* FROM `follows` WHERE `follows`.`followed_id` = 5
SQL (11.2ms) DELETE FROM `users` WHERE `users`.`id` = 5
Mysql2::Error: Cannot delete or update a parent row: a foreign key constraint fails (`inq_development`.`notifications`, CONSTRAINT `fk_rails_c3860515c7` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`)): DELETE FROM `users` WHERE `users`.`id` = 5
(0.5ms) ROLLBACK
ActiveRecord::StatementInvalid: Mysql2::Error: Cannot delete or update a parent row: a foreign key constraint fails (`inq_development`.`notifications`, CONSTRAINT `fk_rails_c3860515c7` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`)): DELETE FROM `users` WHERE `users`.`id` = 5
from /Users/araky/git/inq_rails/vendor/bundle/ruby/2.1.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:299:in `query'
上面，我试图销毁有许多其他对象的用户。 我想如果我们尝试在单个事务上同时删除父行和子行，MySQL会引发错误。 （我听说PostgreSQL正确处理这些情况。）
如何破坏父行？ 我们要删除外国约束？或禁用子模型中设置的相关选项？
什么是最佳做法？