module ActiveRecord
# Callbacks are hooks into the lifecycle of an Active Record object that allow 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 <tt>Base#save</tt> call for a new record:
#
# * (-) <tt>save</tt>
# * (-) <tt>valid</tt>
# * (1) <tt>before_validation</tt>
# * (-) <tt>validate</tt>
# * (-) <tt>validate_on_create</tt>
# * (2) <tt>after_validation</tt>
# * (3) <tt>before_save</tt>
# * (4) <tt>before_create</tt>
# * (-) <tt>create</tt>
# * (5) <tt>after_create</tt>
# * (6) <tt>after_save</tt>
#
# That's a total of eight callbacks, which gives you immense power to react and prepare for each state in the
# Active Record lifecycle. The sequence for calling <tt>Base#save</tt> for an existing record is similar, except that each
# <tt>_on_create</tt> callback is replaced by the corresponding <tt>_on_update</tt> callback.
#
# 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 overwritable 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 <tt>Topic#destroy</tt> is run only +destroy_author+ is called. When <tt>Reply#destroy</tt> is run, both +destroy_author+ and
# +destroy_readers+ are 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, <tt>Reply#destroy</tt> 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 use the regular overwriteable methods
# when you want to leave it up to each descendant 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
# after_save EncryptionWrapper.new
# after_initialize EncryptionWrapper.new
# end
#
# class EncryptionWrapper
# 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. You can make these callbacks more flexible by passing in other
# initialization data such as the name of the attribute to work with:
#
# 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.send("#{@attribute}=", encrypt(record.send("#{@attribute}")))
# end
#
# def after_save(record)
# record.send("#{@attribute}=", decrypt(record.send("#{@attribute}")))
# end
#
# alias_method :after_find, :after_save
#
# private
# def encrypt(value)
# # Secrecy is committed
# end
#
# def decrypt(value)
# # Secrecy is unveiled
# end
# end
#
# 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 quotes (') are used so the <tt>#{id}</tt> 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 <tt>Base.find(:all)</tt>, 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.
#
# == <tt>before_validation*</tt> returning statements
#
# If the returning value of a +before_validation+ callback can be evaluated to +false+, the process will be aborted and <tt>Base#save</tt> will return +false+.
# If Base#save! is called it will raise a ActiveRecord::RecordInvalid exception.
# Nothing will be appended to the errors object.
#
# == Canceling callbacks
#
# If a <tt>before_*</tt> callback returns +false+, all the later callbacks and the associated action are cancelled. If an <tt>after_*</tt> 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.
#
# == Transactions
#
# The entire callback chain of a +save+, <tt>save!</tt>, or +destroy+ call runs
# within a transaction. That includes <tt>after_*</tt> hooks. If everything
# goes fine a COMMIT is executed once the chain has been completed.
#
# If a <tt>before_*</tt> callback cancels the action a ROLLBACK is issued. You
# can also trigger a ROLLBACK raising an exception in any of the callbacks,
# including <tt>after_*</tt> hooks. Note, however, that in that case the client
# needs to be aware of it because an ordinary +save+ will raise such exception
# instead of quietly returning +false+.
module Callbacks
extend ActiveSupport::Concern
CALLBACKS = [
:after_initialize, :after_find, :before_validation, :after_validation,
:before_save, :around_save, :after_save, :before_create, :around_create,
:after_create, :before_update, :around_update, :after_update,
:before_destroy, :around_destroy, :after_destroy
]
included do
[:create_or_update, :valid?, :create, :update, :destroy].each do |method|
alias_method_chain method, :callbacks
end
extend ActiveModel::Callbacks
define_model_callbacks :initialize, :find, :only => :after
define_model_callbacks :save, :create, :update, :destroy
define_model_callbacks :validation, :only => [:before, :after]
end
module ClassMethods
def method_added(meth)
super
if CALLBACKS.include?(meth.to_sym)
ActiveSupport::Deprecation.warn("Base##{meth} has been deprecated, please use Base.#{meth} :method instead", caller[0,1])
send(meth.to_sym, meth.to_sym)
end
end
end
def create_or_update_with_callbacks #:nodoc:
_run_save_callbacks do
create_or_update_without_callbacks
end
end
private :create_or_update_with_callbacks
def create_with_callbacks #:nodoc:
_run_create_callbacks do
create_without_callbacks
end
end
private :create_with_callbacks
def update_with_callbacks(*args) #:nodoc:
_run_update_callbacks do
update_without_callbacks(*args)
end
end
private :update_with_callbacks
def valid_with_callbacks? #:nodoc:
@_on_validate = new_record? ? :create : :update
_run_validation_callbacks do
valid_without_callbacks?
end
end
def destroy_with_callbacks #:nodoc:
_run_destroy_callbacks do
destroy_without_callbacks
end
end
def deprecated_callback_method(symbol) #:nodoc:
if respond_to?(symbol)
ActiveSupport::Deprecation.warn("Overwriting #{symbol} in your models has been deprecated, please use Base##{symbol} :method_name instead")
send(symbol)
end
end
end
end
