The document summarizes key topics from a Ruby on Rails lab on active record associations. It discusses how to add and delete orders, use primary and foreign keys to connect models, and the different types of associations like has_one, has_many, belongs_to, and has_and_belongs_to_many. It also covers association options, polymorphic associations, self joins, counter caches, and the :touch option.

1. The 7th Round of ROR Lab.
Active Record
Associations - 1
February 18th, 2012
Hyoseong Choi
ROR Lab.

2. For what?
ROR Lab.

3. For what?
To add an order
ROR Lab.

4. For what?
To add an order
ROR Lab.

5. For what?
To add an order
To delete orders
ROR Lab.

6. For what?
To add an order
To delete orders
ROR Lab.

7. For what?
• Automation of connecting btw models
• Automatic assignment of foreign key
ROR Lab.

8. For what?
Primary & Foreign Keys
customer order
id id
ROR Lab.

9. For what?
Primary & Foreign Keys
customer order
id id
customer_id
parent obj. child obj.
ROR Lab.

10. For what?
Primary & Foreign Keys
customer order
id id
Active Record customer_id
Assocation
parent obj. child obj.
ROR Lab.

11. For what?
ROR Lab.

12. For what?
To add an order
ROR Lab.

13. For what?
To add an order
ROR Lab.

14. For what?
To add an order
To delete orders
ROR Lab.

15. For what?
To add an order
To delete orders
ROR Lab.

16. Associations
Parent Class Child Class
has_one
1 :1 belongs_to
has_one, :through
1 :n has_many belongs_to
has_many
A
has_many B, :through
belongs_to
n :m has_many
B
has_many A, :through
has_and_belongs_to_many
ROR Lab.

17. Association Options
belongs_to options has_one options has_many options HABTM options
• :autosave • :as • :as • :association_foreign_key
• :class_name • :autosave • :autosave • :autosave
• :conditions • :class_name • :class_name • :class_name
• :counter_cache • :conditions • :conditions • :conditions
• :dependent • :dependent • :counter_sql • :counter_sql
• :foreign_key • :foreign_key • :dependent • :delete_sql
• :include • :include • :extend • :extend
• :polymorphic • :order • :finder_sql • :finder_sql
• :readonly • :primary_key • :foreign_key • :foreign_key
• :select • :readonly • :group • :group
• :touch • :select • :include • :include
• :validate • :source • :limit • :insert_sql
• :source_type • :offset • :join_table
• :through • :order • :limit
• :validate • :primary_key • :offset
• :readonly • :order
• :select • :readonly
• :source • :select
• :source_type • :uniq
• :through • :validate
• :uniq
• :validate
ROR Lab.

18. belongs_to vs
has_one
• “belongs_to” model has a foreign key
• dependent upon the actual meaning of data
ROR Lab.

19. has_many :through vs
has_and_belongs_to_many
๏ has_many
- validations, callbacks, or extra attributes
๏ has_and_belongs_to_many
- no need for additional functionalities
- should create a “join” table in the DB.
ROR Lab.

20. Join Table
HABTM
• Default join table btw Customer & Order
models
: custormers_orders
• Otherwise,
:join_table => “join_table_name”
ROR Lab.

21. Join Table
HABTM
ROR Lab.

22. Join Table
HABTM
no need for join model
ROR Lab.

23. Polymorphic
Employee
id
Product
id
ROR Lab.

24. Polymorphic
Employee Picture
id
Product
id
ROR Lab.

25. Polymorphic
Employee Picture
id employee_id
Product
id
ROR Lab.

26. Polymorphic
Employee Picture
id employee_id
Product Picture
id
ROR Lab.

27. Polymorphic
Employee Picture
id employee_id
Product Picture
id product_id
ROR Lab.

28. Polymorphic
Employee Picture
id employee_id
x
Product Picture
id product_id
ROR Lab.

29. Polymorphic
Imageable Picture
id imageable_id
Imageable Picture
id imageable_id
ROR Lab.

30. Polymorphic
Imageable Picture
Employee
id id imageable_id
Imageable Picture
Product
id id imageable_id
ROR Lab.

31. Polymorphic
Model Class
ROR Lab.

32. Polymorphic
Migration
ROR Lab.

33. Self Joins
• ex. : following or follower
ROR Lab.

34. Screencast
for Self Join
Please click the above link
ROR Lab.

35. :include
• To eager-load the second-order association
ROR Lab.

36. :include
• To eager-load the second-order association
@line_item.order.customer
ROR Lab.

37. :include
• To eager-load the second-order association
@line_item.order.customer
ROR Lab.

38. :counter_cache
NT(*) from ...
ROR Lab.

39. :counter_cache
@customer.orders.size
NT(*) from ...
ROR Lab.

40. :counter_cache
@customer.orders.size
SELECT COUNT(*) from ...
ROR Lab.

41. :counter_cache
@customer.orders.size
SELECT COUNT(*) from ...
ROR Lab.

42. :counter_cache
• But, you should add “orders_count”
column to Customer model
• You can override the default column name.
• ReadOnly !!!
ROR Lab.

43. :counter_cache
• But, you should add “orders_count”
column to Customer model
• You can override the default column name.
• ReadOnly !!!
ROR Lab.

44. Screencast for
Belongs_to
:counter_cache
Please click the above link
ROR Lab.

45. :touch
• Automatically set :updated_at
or :update_on to current timestamp
whenever child objects are saved or
updated
ROR Lab.

46. :touch
ROR Lab.

47. :touch
ROR Lab.

48. :touch
Or using a custom attribute
ROR Lab.

49. :touch
Or using a custom attribute
ROR Lab.

50. 감사합니다.
ROR Lab.