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 Base#save call for a new record: # # * (-) save # * (-) valid # * (1) before_validation # * (-) validate # * (-) validate_on_create # * (2) after_validation # * (3) before_save # * (4) before_create # * (-) create # * (5) after_create # * (6) 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. The sequence for calling Base#save for an existing record is similar, except that each # _on_create callback is replaced by the corresponding _on_update 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 Topic#destroy is run only +destroy_author+ is called. When Reply#destroy 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, 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 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 #{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 (def after_find). 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 ActiveRecord::RecordInvalid exception. # Nothing will be appended to the errors object. # # == Canceling 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. # # == Transactions # # The entire callback chain of a +save+, save!, or +destroy+ call runs # within a transaction. That includes after_* hooks. If everything # goes fine a COMMIT is executed once the chain has been completed. # # If a before_* callback cancels the action a ROLLBACK is issued. You # can also trigger a ROLLBACK raising an exception in any of the callbacks, # including after_* 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