ActiveRecord Anti-Patterns

Transcript

1. Anti-Patterns for fun and profit Active Record Friday, November 4, 2011
2. Ethan Gunderson @ethangunderson Friday, November 4, 2011
3. Friday, November 4, 2011
4. 20% 80% Friday, November 4, 2011
5. Order.all.slice(0, N).select{ |order| order.status == ‘open’} Friday, November 4, 2011
6. Common Mistakes Friday, November 4, 2011
7. ActiveRecord Safari Friday, November 4, 2011
8. “All non-trivial abstractions, to some degree, are leaky.” - Joel Spolsky Friday, November 4, 2011
9. Order.all.slice(0, N).select{ |order| order.status == ‘open’} Friday, November 4, 2011
10. class Order < ActiveRecord::Base scope :open, where(:status => ‘open’) end Order.open.limit(5) Friday, November 4, 2011
11. change_table(:users) do |table| table.string :email table.string :status end Migrations Friday, November 4, 2011
12. 1. Write lock the table. 2. Make a copy of the table. 3. Make changes to the copy. 4. Promote copy to primary. 5. Repeat 1-4. Friday, November 4, 2011
13. connection.execute(“ALTER TABLE `users` ADD COLUMN email varchar(255) DEFAULT NULL, ADD COLUMN status varchar(10) DEFAULT NULL”) Friday, November 4, 2011
14. change_table(:users, :bulk => true) do |table| table.string :email table.string :status end Friday, November 4, 2011
15. The Leaks, they add up. Friday, November 4, 2011
16. Not Optimizing Queries Friday, November 4, 2011
17. Order.all.each do |order| #something end Friday, November 4, 2011
18. Order.all.each do |order| #something end Ouch Friday, November 4, 2011
19. Iterate over the DB cursor and construct an array of rows. Initiate an array of ActiveRecord objects. Friday, November 4, 2011
20. Order.find_each do |order| #something end Friday, November 4, 2011
21. Order.find_in_batches do |orders| #something end Friday, November 4, 2011
22. N + 1 Order.all.each do |order| order.user.first_name end Friday, November 4, 2011
23. N*OMG Order.all.each do |order| order.user.first_name order.user.address.street ... end Friday, November 4, 2011
24. 1 Order.all.includes(:user).each do |order| order.user.first_name end Friday, November 4, 2011
25. Order.all.includes(:user => :address) each do |order| order.user.first_name order.user.address.street ... end Friday, November 4, 2011
26. https://github.com/nesquena/ query_reviewer Friday, November 4, 2011
27. if Object.const_defined?('ActiveRecord') ActiveRecord::Base.logger = Logger.new (STDOUT) end In your ~/.irbrc... Friday, November 4, 2011
28. Race Conditions Friday, November 4, 2011
29. validates_uniqueness_of Friday, November 4, 2011
30. Works. Until you hit production. Friday, November 4, 2011
31. User 1 Checks for uniqueness User 2 Friday, November 4, 2011
32. User 1 Checks for uniqueness User 2 Checks for uniqueness Friday, November 4, 2011
33. User 1 Inserts record User 2 Inserts record Checks for uniqueness Checks for uniqueness Friday, November 4, 2011
34. Success! Friday, November 4, 2011
35. Success! Danger! Friday, November 4, 2011
36. create_index :users, :email, :unique => true Friday, November 4, 2011
37. github.com/trptcolin/consistency_fail Friday, November 4, 2011
38. Abusive Callbacks Friday, November 4, 2011
39. Loading Associations Friday, November 4, 2011
40. class Order < ActiveRecord::Base validate :validate_cc_record def validate_cc_record cc.user != user end end Friday, November 4, 2011
41. Take advantage of dirty attributes Friday, November 4, 2011
42. class Order < ActiveRecord::Base validate :validate_cc_record def validate_cc_record return unless cc_id.changed? cc.user != user end end Friday, November 4, 2011
43. class Order < ActiveRecord::Base before_save :update_item_count def update_sold_count item.increment_sold_count(1) end end Friday, November 4, 2011
44. This is slow Friday, November 4, 2011
45. This is *really* hard to debug in a large application. Friday, November 4, 2011
46. Order Item Vendor Sales Friday, November 4, 2011
47. Order Item Vendor Sales Save fails, returns false Friday, November 4, 2011
48. Order Item Vendor Sales Save fails, returns false Friday, November 4, 2011
49. Keep callbacks simple. Friday, November 4, 2011
50. Breaking the Law Friday, November 4, 2011
51. Demeter Friday, November 4, 2011
52. Each unit should have only limited knowledge about other units: only units "closely" related to the current unit. Each unit should only talk to its friends; don't talk to strangers. Only talk to your immediate friends. Friday, November 4, 2011
53. You can play with yourself. You can play with your toys. You can play with toys given to you. You can play with toys you’ve made yourself. http://c2.com/cgi/wiki?LawOfDemeter Friday, November 4, 2011
54. order.user.address Friday, November 4, 2011
55. But why do I care? Friday, November 4, 2011
56. Coupling Friday, November 4, 2011
57. 0 25 50 75 100 Coupling Cost of Change Friday, November 4, 2011
58. order.user.address Friday, November 4, 2011
59. class Order < ActiveRecord::Base delegate :address, :to => :user, :prefix => true, :allow_nil => true end Friday, November 4, 2011
60. order.user_address Friday, November 4, 2011
61. class Order < ActiveRecord::Base def user_address #different implementation end end Friday, November 4, 2011
62. Recap Friday, November 4, 2011
63. Pay attention to the abstraction Friday, November 4, 2011
64. Optimize those queries Friday, November 4, 2011
65. Avoid complicated callbacks Friday, November 4, 2011
66. Itʼs the law. Follow it. Friday, November 4, 2011
67. The database is your friend. Friday, November 4, 2011
68. YMMV Friday, November 4, 2011
69. Thanks! Friday, November 4, 2011