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
# * (4) after_validation
# * (5) after_validation_on_create
# * (6) before_save
# * (7) before_create
# * (-) create
# * (8) after_create
# * (9) after_save
#
# That's a total of nine callbacks, which gives you immense power to react and prepare for each state in the
# Active Record lifecyle.
#
# 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
# # Automatically assign the signup date
# def before_create
# self.signed_up_on = Date.today
# end
# end
#
# class Firm < ActiveRecord::Base
# # Destroys the associated clients and people when the firm is destroyed
# def before_destroy
# Client.destroy_all "client_of = #{id}"
# Person.destroy_all "firm_id = #{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.
#
# == 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 is some times 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_initialize, :after_save
#
# private
# def encrypt(value)
# # Secrecy is committed
# end
#
# def decrypt(value)
# # Secrecy is unvieled
# 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 is called for each object instantiated found 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 can only be declared using an explicit implementation. So using the inheritable callback queue for after_find and
# after_initialize won't work.
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.append_features(base) #:nodoc:
super
base.extend(ClassMethods)
base.class_eval do
class << self
include Observable
alias_method :instantiate_without_callbacks, :instantiate
alias_method :instantiate, :instantiate_with_callbacks
end
end
base.class_eval do
alias_method :initialize_without_callbacks, :initialize
alias_method :initialize, :initialize_with_callbacks
alias_method :create_or_update_without_callbacks, :create_or_update
alias_method :create_or_update, :create_or_update_with_callbacks
alias_method :valid_without_callbacks, :valid?
alias_method :valid?, :valid_with_callbacks
alias_method :create_without_callbacks, :create
alias_method :create, :create_with_callbacks
alias_method :update_without_callbacks, :update
alias_method :update, :update_with_callbacks
alias_method :destroy_without_callbacks, :destroy
alias_method :destroy, :destroy_with_callbacks
end
CALLBACKS.each { |cb| base.class_eval("def self.#{cb}(*methods) write_inheritable_array(\"#{cb}\", methods) end") }
end
module ClassMethods #:nodoc:
def instantiate_with_callbacks(record)
object = instantiate_without_callbacks(record)
object.callback(:after_find) if object.respond_to_without_attributes?(:after_find)
object.callback(:after_initialize) if object.respond_to_without_attributes?(:after_initialize)
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)
yield self if block_given?
after_initialize if respond_to_without_attributes?(:after_initialize)
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).
def after_save() end
def create_or_update_with_callbacks #:nodoc:
callback(:before_save)
create_or_update_without_callbacks
callback(:after_save)
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:
callback(:before_create)
create_without_callbacks
callback(:after_create)
end
# Is called _before_ Base.save on existing objects that has a record.
def before_update() end
# Is called _after_ Base.save on existing objects that has a record.
def after_update() end
def update_with_callbacks #:nodoc:
callback(:before_update)
update_without_callbacks
callback(:after_update)
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 has 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 has a record.
def after_validation_on_update() end
def valid_with_callbacks #:nodoc:
callback(:before_validation)
if new_record? then callback(:before_validation_on_create) else callback(:before_validation_on_update) end
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.
def before_destroy() end
# Is called _after_ Base.destroy (and all the attributes have been frozen).
def after_destroy() end
def destroy_with_callbacks #:nodoc:
callback(:before_destroy)
destroy_without_callbacks
callback(:after_destroy)
end
def callback(callback_method) #:nodoc:
run_callbacks(callback_method)
send(callback_method)
notify(callback_method)
end
def run_callbacks(callback_method)
filters = self.class.read_inheritable_attribute(callback_method.to_s)
if filters.nil? then return end
filters.each do |filter|
if Symbol === filter
self.send(filter)
elsif String === filter
eval(filter, binding)
elsif filter_block?(filter)
filter.call(self)
elsif filter_class?(filter, callback_method)
filter.send(callback_method, self)
else
raise(
ActiveRecordError,
"Filters need to be either a symbol, string (to be eval'ed), proc/method, or " +
"class implementing a static filter method"
)
end
end
end
def filter_block?(filter)
filter.respond_to?("call") && (filter.arity == 1 || filter.arity == -1)
end
def filter_class?(filter, callback_method)
filter.respond_to?(callback_method)
end
def notify(callback_method) #:nodoc:
self.class.changed
self.class.notify_observers(callback_method, self)
end
end
end
