This is a Keynote slide about the "ActiveRecord Callbacks & Observers"

1. Ror lab. season 2
- the 7th round -
Active Record
Callbacks & Observers
October 6th, 2012
Hyoseong Choi

2. Contents
Validations Callbacks
• The Object Life Cycle • Callbacks Overview
• Validations Overview • Available Callbacks
• Validation Helpers • Running Callbacks
• Common Validation • Skipping Callbacks
Options • Halting Execution
• Conditional Validation • Relational Callbacks
• Custom Validations • Conditional Callbacks
• Working with Validation • Callback Classes
Errors
• Observers
• Displaying Validation Errors
• Transaction Callbacks
in the View

3. Life-cycle of
Objects
DB

4. Life-cycle of
Objects
DB
Active
Record
el
od
M

5. Life-cycle of
Active
Record
el Objects
od
M
DB
Create Save
Object
Delete Update

6. Life-cycle of
Active
Record
el Objects
od
M
DB
Create Save
Validation
Object
Delete Update
load

7. Callbacks
• Methods : protected or private
• Before or after certain moments of an
object’s life cycle
• 6create, save, update, delete, validate, load
:
events
• Register using a macro-style class method
★ as an ordinary method or
★ supply as a block

8. Available Callbacks
★ Creating an Object ★ Updating an Object ★ Destroying an Object
• before_validation • before_validation • before_destroy
• after_validation • after_validation • around_destroy
• before_save • before_save • after_destroy
• before_create • before_update
• around_create • around_update
• after_create • after_update
• after_save • after_save
DB
Validation
Create
Save
Update
Destroy

9. After_find
> After_initialize
class User < ActiveRecord::Base
after_initialize do |user|
puts "You have initialized an object!"
end
after_find do |user|
puts "You have found an object!"
end
end
>> User.new
You have initialized an object!
=> #<User id: nil>
>> User.first
You have found an object!
You have initialized an object!
=> #<User id: 1>

10. Methods
Triggering Callbacks
•
•
create
create!
‘after_find’ callback
• decrement! • all
• destroy • first
• destroy_all • find
• increment! • find_all_by_attribute
• save • find_by_attribute
• save!
• find_by_attribute!
• save(:validate =>false)
• toggle! • last
• update
• update_attribute
• update_attributes
• update_attributes!
• valid?

11. Methods
Skipping Callbacks
• decrement
• decrement_counter
• delete
• delete_all
• find_by_sql
• increment
• increment_counter
• toggle
• touch
• update_column
• update_all
• update_counters

12. Methods Calling Callbacks Methods Skipping Callbacks
create
create!
decrement! decrement / ~_counter
destroy delete
destroy_all delete_all
increment! increment / ~_counter
save
save!
save(false)
toggle! toggle
update
update_attribute update_column
update_attributes update_all
update_attributes! update_counters
valid?
find_by_sql
touch

13. Halting Execution
• Queue
★ validations for model
★ registered callbacks
★ database operations
• Wrapped in a Transaction
★ before_ callbacks
: false or exception > stopped > ROLLBACK
★ after_ callbacks
: exception > stopped > ROLLBACK

14. Relational
Callbacks

15. Conditional
Callbacks
• As with validations
★ Using :if and :unless with a Symbol
★ Using :if and :unless with a String
★ Using :if and :unless with a Proc

16. Conditional
Callbacks
as a symbol
as a string
as a Proc
* multiple conditions possible!

17. Callback Classes
• To reuse callback methods for other models
as an instance method
a model object
instance
method

18. Callback Classes
as a class method

19. Observers
• Similar to callbacks
• for the callbacks with the code that isn’t
directly related the model
• without changing the code of the model
• ex. sending confirmation email after user
registration

20. Creating Observers

21. Registering Observers
• config/application.rb
• or config/environments

22. Sharing Observers
as a model name

23. Transaction
Callbacks
• after_commit or after_rollback

24. 감사합니다.

26. Macro-style class methods :
As Ordinary
Methods
class User ActiveRecord::Base
validates :login, :email, :presence = true
before_validation :ensure_login_has_a_value
protected
def ensure_login_has_a_value
if login.nil?
self.login = email unless email.blank?
end
end

27. public/protected/private
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http://stackoverflow.com/questions/4495078/protected-and-private-methods-in-rails

28. Macro-style class methods :
A Block
class User ActiveRecord::Base
validates :login, :email, :presence = true
before_create do |user|
user.name = user.login.capitalize
if user.name.blank?
end