Module: ActiveRecord::Callbacks
- Defined in:
- lib/active_record/callbacks.rb
Overview
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() 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 (def after_find
). In that case, all of the callback types will be called.
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.
Defined Under Namespace
Modules: ClassMethods
Constant Summary collapse
- 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 )
Class Method Summary collapse
-
.append_features(base) ⇒ Object
:nodoc:.
Instance Method Summary collapse
-
#after_create ⇒ Object
Is called after Base.save on new objects that haven’t been saved yet (no record exists).
-
#after_destroy ⇒ Object
Is called after Base.destroy (and all the attributes have been frozen).
-
#after_save ⇒ Object
Is called after Base.save (regardless of whether it’s a create or update save).
-
#after_update ⇒ Object
Is called after Base.save on existing objects that have a record.
-
#after_validation ⇒ Object
Is called after Validations.validate (which is part of the Base.save call).
-
#after_validation_on_create ⇒ Object
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).
-
#after_validation_on_update ⇒ Object
Is called after Validations.validate (which is part of the Base.save call) on existing objects that have a record.
-
#before_create ⇒ Object
Is called before Base.save on new objects that haven’t been saved yet (no record exists).
-
#before_destroy ⇒ Object
Is called before Base.destroy.
-
#before_save ⇒ Object
Is called before Base.save (regardless of whether it’s a create or update save).
-
#before_update ⇒ Object
Is called before Base.save on existing objects that have a record.
-
#before_validation ⇒ Object
Is called before Validations.validate (which is part of the Base.save call).
-
#before_validation_on_create ⇒ Object
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).
-
#before_validation_on_update ⇒ Object
Is called before Validations.validate (which is part of the Base.save call) on existing objects that have a record.
-
#create_or_update_with_callbacks ⇒ Object
:nodoc:.
-
#create_with_callbacks ⇒ Object
:nodoc:.
-
#destroy_with_callbacks ⇒ Object
:nodoc:.
-
#initialize_with_callbacks(attributes = nil) ⇒ Object
Is called after the object has been instantiated by a call to Base.new.
-
#update_with_callbacks ⇒ Object
:nodoc:.
-
#valid_with_callbacks ⇒ Object
:nodoc:.
Class Method Details
.append_features(base) ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 173 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 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 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 |
Instance Method Details
#after_create ⇒ Object
Is called after Base.save on new objects that haven’t been saved yet (no record exists).
258 |
# File 'lib/active_record/callbacks.rb', line 258 def after_create() end |
#after_destroy ⇒ Object
Is called after Base.destroy (and all the attributes have been frozen).
318 |
# File 'lib/active_record/callbacks.rb', line 318 def after_destroy() end |
#after_save ⇒ Object
Is called after Base.save (regardless of whether it’s a create or update save).
246 |
# File 'lib/active_record/callbacks.rb', line 246 def after_save() end |
#after_update ⇒ Object
Is called after Base.save on existing objects that have a record.
270 |
# File 'lib/active_record/callbacks.rb', line 270 def after_update() end |
#after_validation ⇒ Object
Is called after Validations.validate (which is part of the Base.save call).
283 |
# File 'lib/active_record/callbacks.rb', line 283 def after_validation() end |
#after_validation_on_create ⇒ Object
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).
291 |
# File 'lib/active_record/callbacks.rb', line 291 def after_validation_on_create() end |
#after_validation_on_update ⇒ Object
Is called after Validations.validate (which is part of the Base.save call) on existing objects that have a record.
299 |
# File 'lib/active_record/callbacks.rb', line 299 def after_validation_on_update() end |
#before_create ⇒ Object
Is called before Base.save on new objects that haven’t been saved yet (no record exists).
255 |
# File 'lib/active_record/callbacks.rb', line 255 def before_create() end |
#before_destroy ⇒ Object
Is called before Base.destroy.
315 |
# File 'lib/active_record/callbacks.rb', line 315 def before_destroy() end |
#before_save ⇒ Object
Is called before Base.save (regardless of whether it’s a create or update save).
243 |
# File 'lib/active_record/callbacks.rb', line 243 def before_save() end |
#before_update ⇒ Object
Is called before Base.save on existing objects that have a record.
267 |
# File 'lib/active_record/callbacks.rb', line 267 def before_update() end |
#before_validation ⇒ Object
Is called before Validations.validate (which is part of the Base.save call).
280 |
# File 'lib/active_record/callbacks.rb', line 280 def before_validation() end |
#before_validation_on_create ⇒ Object
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).
287 |
# File 'lib/active_record/callbacks.rb', line 287 def before_validation_on_create() end |
#before_validation_on_update ⇒ Object
Is called before Validations.validate (which is part of the Base.save call) on existing objects that have a record.
295 |
# File 'lib/active_record/callbacks.rb', line 295 def before_validation_on_update() end |
#create_or_update_with_callbacks ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 247 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 |
#create_with_callbacks ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 259 def create_with_callbacks #:nodoc: return false if callback(:before_create) == false result = create_without_callbacks callback(:after_create) result end |
#destroy_with_callbacks ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 319 def destroy_with_callbacks #:nodoc: return false if callback(:before_destroy) == false result = destroy_without_callbacks callback(:after_destroy) result end |
#initialize_with_callbacks(attributes = nil) ⇒ Object
Is called after the object has been instantiated by a call to Base.new. def after_initialize() end
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# File 'lib/active_record/callbacks.rb', line 235 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 |
#update_with_callbacks ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 272 def update_with_callbacks #:nodoc: return false if callback(:before_update) == false result = update_without_callbacks callback(:after_update) result end |
#valid_with_callbacks ⇒ Object
:nodoc:
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# File 'lib/active_record/callbacks.rb', line 301 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 |