--- /dev/null
+require 'observer'
+
+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>
+ # * (2) <tt>before_validation_on_create</tt>
+ # * (-) <tt>validate</tt>
+ # * (-) <tt>validate_on_create</tt>
+ # * (3) <tt>after_validation</tt>
+ # * (4) <tt>after_validation_on_create</tt>
+ # * (5) <tt>before_save</tt>
+ # * (6) <tt>before_create</tt>
+ # * (-) <tt>create</tt>
+ # * (7) <tt>after_create</tt>
+ # * (8) <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> 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 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 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
+ 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 Observable
+
+ [:create_or_update, :valid?, :create, :update, :destroy].each do |method|
+ base.send :alias_method_chain, method, :callbacks
+ end
+
+ base.send :include, ActiveSupport::Callbacks
+ base.define_callbacks *CALLBACKS
+ end
+
+ # Is called when the object was instantiated by one of the finders, like <tt>Base.find</tt>.
+ #def after_find() end
+
+ # Is called after the object has been instantiated by a call to <tt>Base.new</tt>.
+ #def after_initialize() end
+
+ # Is called _before_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
+ def before_save() end
+
+ # Is called _after_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
+ # Note that this callback is still wrapped in the transaction around +save+. For example, if you
+ # invoke an external indexer at this point it won't see the changes in the database.
+ #
+ # 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
+ private :create_or_update_with_callbacks
+
+ # Is called _before_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
+ def before_create() end
+
+ # Is called _after_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
+ # Note that this callback is still wrapped in the transaction around +save+. For example, if you
+ # invoke an external indexer at this point it won't see the changes in the database.
+ 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
+ private :create_with_callbacks
+
+ # Is called _before_ <tt>Base.save</tt> on existing objects that have a record.
+ def before_update() end
+
+ # Is called _after_ <tt>Base.save</tt> on existing objects that have a record.
+ # Note that this callback is still wrapped in the transaction around +save+. For example, if you
+ # invoke an external indexer at this point it won't see the changes in the database.
+ def after_update() end
+
+ def update_with_callbacks(*args) #:nodoc:
+ return false if callback(:before_update) == false
+ result = update_without_callbacks(*args)
+ callback(:after_update)
+ result
+ end
+ private :update_with_callbacks
+
+ # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
+ def before_validation() end
+
+ # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
+ def after_validation() end
+
+ # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
+ # that haven't been saved yet (no record exists).
+ def before_validation_on_create() end
+
+ # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
+ # that haven't been saved yet (no record exists).
+ def after_validation_on_create() end
+
+ # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on
+ # existing objects that have a record.
+ def before_validation_on_update() end
+
+ # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> 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 false == result
+
+ 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_ <tt>Base.destroy</tt>.
+ #
+ # Note: If you need to _destroy_ or _nullify_ associated records first,
+ # use the <tt>:dependent</tt> option on your associations.
+ def before_destroy() end
+
+ # Is called _after_ <tt>Base.destroy</tt> (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)
+ result = run_callbacks(method) { |result, object| false == result }
+
+ if result != false && respond_to_without_attributes?(method)
+ result = send(method)
+ end
+
+ notify(method)
+
+ return result
+ end
+
+ def notify(method) #:nodoc:
+ self.class.changed
+ self.class.notify_observers(method, self)
+ end
+ end
+end
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