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