This is a Keynote slide about the "ActiveRecord Association (1)"

1. Ror lab. season 2
- the 8th round -
Active Record
Associations (1)
October 20th, 2012
Hyoseong Choi

2. No Associations

3. No Associations
To add an order

4. No Associations
To add an order
To delete a customer

5. The Reason why
we should use
Active Record
Associations
• Automation of connecting btw models
• Automatic assignment of foreign key

6. Using Active Record
Associations
Primary & Foreign Keys
customer order
id id

7. Using Active Record
Associations
Primary & Foreign Keys
customer order
id id
customer_id
parent obj. child obj.

8. Using Active Record
Associations
Primary & Foreign Keys
customer order
id id
Active Record customer_id
Assocation
parent obj. child obj.

9. With Associations

10. With Associations
To add an order

11. With Associations
To add an order
To delete a customer

12. Associations
Parent Class Child Class
has_one
1 :1 belongs_to
has_one, :through
1 :n has_many belongs_to
has_many
A C
has_many B, :through
n :m has_many belongs_to
B
has_many A, :through
A/B has_and_belongs_to_many

13. 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

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

15. 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.

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

17. Join Table
HABTM

18. Join Table
HABTM
no need for join model

19. Polymorphic
Employee
id
Product
id

20. Polymorphic
Employee Picture
id
Product
id

21. Polymorphic
Employee Picture
id employee_id
Product
id

22. Polymorphic
Employee Picture
id employee_id
Product Picture
id

23. Polymorphic
Employee Picture
id employee_id
Product Picture
id product_id

24. Polymorphic
Employee Picture
id employee_id
x
Product Picture
id product_id

25. Polymorphic
What about this “Picture” model ?
Employee Product
id id

26. Polymorphic
What about this “Picture” model ?
Employee Picture Product
id employee_id id
product_id

27. Polymorphic
What about this “Picture” model ?
Employee Picture Product Picture
id employee_id id product_id
product_id employee_id

28. Polymorphic
What about this “Picture” model ?
Employee Picture Product Picture
id employee_id id product_id
product_id employee_id

29. Polymorphic
Picture
Employee
id
Picture
Product
id

30. Polymorphic
Picture
Employee
id
:as => :imageable
Picture
Product
id

31. Polymorphic
Imageable Picture
Employee
id id
Imageable Picture
Product
id id

32. Polymorphic
Imageable Picture
Employee
:imageable_type
id id imageable_id
:imageable_id
Imageable Picture
Product
id id imageable_id

33. Polymorphic
Model Class

34. Polymorphic
Migration

35. Self Joins
• ex. : following or follower

36. Screencast
for Self Join
Please click the above link

37. :include
• To eager-load the second-order association

38. :include
• To eager-load the second-order association
@line_item.order.customer

39. :include
• To eager-load the second-order association
@line_item.order.customer

40. :counter_cache
NT(*) from ...

41. :counter_cache
@customer.orders.size
NT(*) from ...

42. :counter_cache
@customer.orders.size
SELECT COUNT(*) from ...

43. :counter_cache
@customer.orders.size
SELECT COUNT(*) from ...

44. :counter_cache
• But, you should add “orders_count” column to Customer model
• Default column name : table name + “_count”
• You can override the default column name.
• ReadOnly !!!

45. :counter_cache
• But, you should add “orders_count” column to Customer model
• Default column name : table name + “_count”
• You can override the default column name.
• ReadOnly !!!

46. Screencast for
Belongs_to
:counter_cache
Please click the above link

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

48. :touch

49. :touch

50. :touch
Or using a custom attribute

51. :touch
Or using a custom attribute

52. 감사합니다.