Rails talk - RubyLightningTalksTO

Common Rails mistakes, and things you should probably avoid

Transcript

1. COMMON RAILS MISTAKES AND THINGS YOU SHOULD PROBABLY AVOID
2. ▸ I work at GitHub ▸ ❤ Open source ▸ rubygems.org maintainer ▸ Part of the Rails committer team ▸ GPG fingerprint: 1E433E17
3. CALLBACKS
4. MODEL CALLBACKS : KEY POINTS ▸ Most of them run inside a transaction. ▸ The returned value matters. ▸ `before_destroy { return false }` ▸ Rails uses and sets some default callbacks. ▸ `has_many :assets, dependent: :destroy` CALLBACKS
5. DB TRANSACTION - TRADEOFF CONSISTENCY SPEED In the database’s point of view: consistency > speed
6. COMMON MISTAKES: ▸ Postpone things to run on jobs. ▸ Data integrity issues. ▸ I/O calls in callbacks. ▸ Performance issues. CALLBACKS
7. CALLBACKS 1 class User < ActiveRecord::Base 2 after_save :update_friends_count 3 def update_friends_count 4 FriendsCounterJob.perform_later(self) 5 end 6 7 after_save :upload_avatar 8 def upload_avatar 9 S3.upload(avatar_url) 10 end 11 end
8. CALLBACKS FIX: ▸ Don’t queue data that needs to be consistent. ▸ callbacks that run after the transaction. ▸ after_commit ▸ after_rollback
9. KEY POINTS ▸ They don’t run inside the transaction. ▸ They run after the transaction. AFTER_COMMIT & AFTER_ROLLBACK
10. CATCHES ▸ They don’t stop the transaction if there is any error ▸ The error doesn’t even get raised. AFTER_COMMIT & AFTER_ROLLBACK
11. AFTER_COMMIT 1 class S3; end 2 def S3.upload(*) 3 raise "IO error" 4 end 5 6 class User < ActiveRecord::Base 7 after_commit :upload_avatar 8 def upload_avatar 9 S3.upload(file) 10 end 11 end 12 13 class BugTest < ActiveSupport::TestCase 14 def test_upload_the_avatar_if_io_error 15 assert_raises { User.create } 16 end 17 end
12. Finished in 0.020805s, 48.0654 runs/s, 48.0654 assertions/s. 1) Failure: BugTest#test_upload_the_avatar_if_io_error [test.rb:15]: [] expected but nothing was raised. AFTER_COMMIT
13. AFTER_COMMIT 1 class S3; end 2 def S3.upload(*) 3 raise "IO error" 4 end 5 6 class User < ActiveRecord::Base 7 after_commit :upload_avatar 8 def upload_avatar 9 S3.upload(file) 10 end 11 end 12 13 class BugTest < ActiveSupport::TestCase 14 def test_upload_the_avatar_if_io_error 15 assert_raises { User.create } 16 end 17 end
14. AFTER_COMMIT FIX: Rails 4.2 config.active_record.raise_in_transactional_callbacks = true Rails 5+
15. THINGS WE SHOULD AVOID
16. STI : SINGLE TABLE INHERITANCE
17. STI: SINGLE TABLE INHERITANCE 1 class User < ActiveRecord::Base 2 def authenticate(password); end 3 def upload_avatar(file); end 4 def update_code(); end 5 end 6 7 class Organization < User 8 end 9 10 User.create(login: 'arthurnn') 11 Organization.create(login: 'rails')
18. STI ▸ Everything lives in the same table ▸ Hard to scale. ▸ Hard to move away from it. ▸ You don’t need STI for code reuse. PROBLEMS:
19. STI: SINGLE TABLE INHERITANCE DATABASE INDEX PERFORMANCE ▸ Database index search is: O(log N) ▸ Database non-index search: O(N) ▸ `type` column needs to be on most of indexes.
20. 1 module Authenticable 2 def authenticate(password); end 3 end 4 module Avatarable 5 def upload_avatar(file); end 6 end 7 8 class User < ActiveRecord::Base 9 include Authenticable 10 include Avatarable 11 end 12 13 class Organization < ActiveRecord::Base 14 include Authenticable 15 include Avatarable 16 end 17 18 User.create(login: 'arthurnn') 19 Organization.create(login: 'rails') STI: SOLUTION
21. DEFAULT SCOPE
22. DEFAULT SCOPE 1 class Shop < ActiveRecord::Base 2 default_scope { where(deleted: false) } 3 4 def destroy 5 _run_destroy_callbacks do 6 update(deleted: true) 7 end 8 end 9 end 10 11 shop = Shop.find(42) 12 shop.destroy 13 14 Shop.find(42) 15 => nil
23. DEFAULT SCOPE PROBLEMS: ▸ default_scope is too magical. ▸ There is some bugs in rails, still today, on default_scope ▸ Same indexes issues. All the queries need to include scope on the index.
24. DEFAULT SCOPE : SOLUTION 1 class Shop < ActiveRecord::Base 2 before_destroy :archive_record 3 def archive_record 4 ShopArchive.archive_shop(self) 5 end 6 end 7 8 shop = Shop.find(42) 9 shop.destroy 10 11 Shop.find(42) 12 => nil
25. CONCLUSION ▸ Be aware of callbacks magic, and try to understand where and when they run. ▸ Don’t use STI ▸ Don’t use default_scope
26. THANKS @arthurnn