require 'observer'
module ActiveRecord
# Callbacks are hooks into the lifecycle of an Active Record object that allows you to trigger logic
# before or after an alteration of the object state. This can be used to make sure that associated and
# dependent objects are deleted when destroy is called (by overwriting before_destroy) or to massage attributes
# before they're validated (by overwriting before_validation). As an example of the callbacks initiated, consider
# the Base#save call:
#
# * (-) save
# * (-) valid?
# * (1) before_validation
# * (2) before_validation_on_create
# * (-) validate
# * (-) validate_on_create
# * (3) after_validation
# * (4) after_validation_on_create
# * (5) before_save
# * (6) before_create
# * (-) create
# * (7) after_create
# * (8) after_save
#
# That's a total of eight callbacks, which gives you immense power to react and prepare for each state in the
# Active Record lifecycle.
#
# Examples:
# class CreditCard < ActiveRecord::Base
# # Strip everything but digits, so the user can specify "555 234 34" or
# # "5552-3434" or both will mean "55523434"
# def before_validation_on_create
# self.number = number.gsub(/[^0-9]/, "") if attribute_present?("number")
# end
# end
#
# class Subscription < ActiveRecord::Base
# before_create :record_signup
#
# private
# def record_signup
# self.signed_up_on = Date.today
# end
# end
#
# class Firm < ActiveRecord::Base
# # Destroys the associated clients and people when the firm is destroyed
# before_destroy { |record| Person.destroy_all "firm_id = #{record.id}" }
# before_destroy { |record| Client.destroy_all "client_of = #{record.id}" }
# end
#
# == Inheritable callback queues
#
# Besides the overwriteable callback methods, it's also possible to register callbacks through the use of the callback macros.
# Their main advantage is that the macros add behavior into a callback queue that is kept intact down through an inheritance
# hierarchy. Example:
#
# class Topic < ActiveRecord::Base
# before_destroy :destroy_author
# end
#
# class Reply < Topic
# before_destroy :destroy_readers
# end
#
# Now, when Topic#destroy is run only +destroy_author+ is called. When Reply#destroy is run both +destroy_author+ and
# +destroy_readers+ is called. Contrast this to the situation where we've implemented the save behavior through overwriteable
# methods:
#
# class Topic < ActiveRecord::Base
# def before_destroy() destroy_author end
# end
#
# class Reply < Topic
# def before_destroy() destroy_readers end
# end
#
# In that case, Reply#destroy would only run +destroy_readers+ and _not_ +destroy_author+. So use the callback macros when
# you want to ensure that a certain callback is called for the entire hierarchy and the regular overwriteable methods when you
# want to leave it up to each descendent to decide whether they want to call +super+ and trigger the inherited callbacks.
#
# *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the callbacks before specifying the
# associations. Otherwise, you might trigger the loading of a child before the parent has registered the callbacks and they won't
# be inherited.
#
# == Types of callbacks
#
# There are four types of callbacks accepted by the callback macros: Method references (symbol), callback objects,
# inline methods (using a proc), and inline eval methods (using a string). Method references and callback objects are the
# recommended approaches, inline methods using a proc are sometimes appropriate (such as for creating mix-ins), and inline
# eval methods are deprecated.
#
# The method reference callbacks work by specifying a protected or private method available in the object, like this:
#
# class Topic < ActiveRecord::Base
# before_destroy :delete_parents
#
# private
# def delete_parents
# self.class.delete_all "parent_id = #{id}"
# end
# end
#
# The callback objects have methods named after the callback called with the record as the only parameter, such as:
#
# class BankAccount < ActiveRecord::Base
# before_save EncryptionWrapper.new("credit_card_number")
# after_save EncryptionWrapper.new("credit_card_number")
# after_initialize EncryptionWrapper.new("credit_card_number")
# end
#
# class EncryptionWrapper
# def initialize(attribute)
# @attribute = attribute
# end
#
# def before_save(record)
# record.credit_card_number = encrypt(record.credit_card_number)
# end
#
# def after_save(record)
# record.credit_card_number = decrypt(record.credit_card_number)
# end
#
# alias_method :after_find, :after_save
#
# private
# def encrypt(value)
# # Secrecy is committed
# end
#
# def decrypt(value)
# # Secrecy is unveiled
# end
# end
#
# So you specify the object you want messaged on a given callback. When that callback is triggered, the object has
# a method by the name of the callback messaged.
#
# The callback macros usually accept a symbol for the method they're supposed to run, but you can also pass a "method string",
# which will then be evaluated within the binding of the callback. Example:
#
# class Topic < ActiveRecord::Base
# before_destroy 'self.class.delete_all "parent_id = #{id}"'
# end
#
# Notice that single plings (') are used so the #{id} part isn't evaluated until the callback is triggered. Also note that these
# inline callbacks can be stacked just like the regular ones:
#
# class Topic < ActiveRecord::Base
# before_destroy 'self.class.delete_all "parent_id = #{id}"',
# 'puts "Evaluated after parents are destroyed"'
# end
#
# == The after_find and after_initialize exceptions
#
# Because after_find and after_initialize are called for each object found and instantiated by a finder, such as Base.find(:all), we've had
# to implement a simple performance constraint (50% more speed on a simple test case). Unlike all the other callbacks, after_find and
# after_initialize will only be run if an explicit implementation is defined (<tt>def after_find</tt>). In that case, all of the
# callback types will be called.
#
# == before_validation* returning statements
#
# If the returning value of a before_validation callback can be evaluated to false, the process will be aborted and Base#save will return false.
# If Base#save! is called it will raise a RecordNotSave error.
# Nothing will be appended to the errors object.
#
# == Cancelling callbacks
#
# If a before_* callback returns false, all the later callbacks and the associated action are cancelled. If an after_* callback returns
# false, all the later callbacks are cancelled. Callbacks are generally run in the order they are defined, with the exception of callbacks
# defined as methods on the model, which are called last.
module Callbacks
CALLBACKS = %w(
after_find after_initialize before_save after_save before_create after_create before_update after_update before_validation
after_validation before_validation_on_create after_validation_on_create before_validation_on_update
after_validation_on_update before_destroy after_destroy
)
def self.included(base) #:nodoc:
base.extend(ClassMethods)
base.class_eval do
class << self
include Observable
alias_method_chain :instantiate, :callbacks
end
[:initialize, :create_or_update, :valid?, :create, :update, :destroy].each do |method|
alias_method_chain method, :callbacks
end
end
CALLBACKS.each do |method|
base.class_eval <<-"end_eval"
def self.#{method}(*callbacks, &block)
callbacks << block if block_given?
write_inheritable_array(#{method.to_sym.inspect}, callbacks)
end
end_eval
end
end
module ClassMethods #:nodoc:
def instantiate_with_callbacks(record)
object = instantiate_without_callbacks(record)
if object.respond_to_without_attributes?(:after_find)
object.send(:callback, :after_find)
end
if object.respond_to_without_attributes?(:after_initialize)
object.send(:callback, :after_initialize)
end
object
end
end
# Is called when the object was instantiated by one of the finders, like Base.find.
#def after_find() end
# Is called after the object has been instantiated by a call to Base.new.
#def after_initialize() end
def initialize_with_callbacks(attributes = nil) #:nodoc:
initialize_without_callbacks(attributes)
result = yield self if block_given?
callback(:after_initialize) if respond_to_without_attributes?(:after_initialize)
result
end
# Is called _before_ Base.save (regardless of whether it's a create or update save).
def before_save() end
# Is called _after_ Base.save (regardless of whether it's a create or update save).
#
# class Contact < ActiveRecord::Base
# after_save { logger.info( 'New contact saved!' ) }
# end
def after_save() end
def create_or_update_with_callbacks #:nodoc:
return false if callback(:before_save) == false
result = create_or_update_without_callbacks
callback(:after_save)
result
end
# Is called _before_ Base.save on new objects that haven't been saved yet (no record exists).
def before_create() end
# Is called _after_ Base.save on new objects that haven't been saved yet (no record exists).
def after_create() end
def create_with_callbacks #:nodoc:
return false if callback(:before_create) == false
result = create_without_callbacks
callback(:after_create)
result
end
# Is called _before_ Base.save on existing objects that have a record.
def before_update() end
# Is called _after_ Base.save on existing objects that have a record.
def after_update() end
def update_with_callbacks #:nodoc:
return false if callback(:before_update) == false
result = update_without_callbacks
callback(:after_update)
result
end
# Is called _before_ Validations.validate (which is part of the Base.save call).
def before_validation() end
# Is called _after_ Validations.validate (which is part of the Base.save call).
def after_validation() end
# Is called _before_ Validations.validate (which is part of the Base.save call) on new objects
# that haven't been saved yet (no record exists).
def before_validation_on_create() end
# Is called _after_ Validations.validate (which is part of the Base.save call) on new objects
# that haven't been saved yet (no record exists).
def after_validation_on_create() end
# Is called _before_ Validations.validate (which is part of the Base.save call) on
# existing objects that have a record.
def before_validation_on_update() end
# Is called _after_ Validations.validate (which is part of the Base.save call) on
# existing objects that have a record.
def after_validation_on_update() end
def valid_with_callbacks? #:nodoc:
return false if callback(:before_validation) == false
if new_record? then result = callback(:before_validation_on_create) else result = callback(:before_validation_on_update) end
return false if result == false
result = valid_without_callbacks?
callback(:after_validation)
if new_record? then callback(:after_validation_on_create) else callback(:after_validation_on_update) end
return result
end
# Is called _before_ Base.destroy.
#
# Note: If you need to _destroy_ or _nullify_ associated records first,
# use the _:dependent_ option on your associations.
def before_destroy() end
# Is called _after_ Base.destroy (and all the attributes have been frozen).
#
# class Contact < ActiveRecord::Base
# after_destroy { |record| logger.info( "Contact #{record.id} was destroyed." ) }
# end
def after_destroy() end
def destroy_with_callbacks #:nodoc:
return false if callback(:before_destroy) == false
result = destroy_without_callbacks
callback(:after_destroy)
result
end
private
def callback(method)
notify(method)
callbacks_for(method).each do |callback|
result = case callback
when Symbol
self.send(callback)
when String
eval(callback, binding)
when Proc, Method
callback.call(self)
else
if callback.respond_to?(method)
callback.send(method, self)
else
raise ActiveRecordError, "Callbacks must be a symbol denoting the method to call, a string to be evaluated, a block to be invoked, or an object responding to the callback method."
end
end
return false if result == false
end
result = send(method) if respond_to_without_attributes?(method)
return result
end
def callbacks_for(method)
self.class.read_inheritable_attribute(method.to_sym) or []
end
def invoke_and_notify(method)
notify(method)
send(method) if respond_to_without_attributes?(method)
end
def notify(method) #:nodoc:
self.class.changed
self.class.notify_observers(method, self)
end
end
end
