4 # Callbacks are hooks into the lifecycle of an Active Record object that allow you to trigger logic
5 # before or after an alteration of the object state. This can be used to make sure that associated and
6 # dependent objects are deleted when +destroy+ is called (by overwriting +before_destroy+) or to massage attributes
7 # before they're validated (by overwriting +before_validation+). As an example of the callbacks initiated, consider
8 # the <tt>Base#save</tt> call for a new record:
11 # * (-) <tt>valid</tt>
12 # * (1) <tt>before_validation</tt>
13 # * (2) <tt>before_validation_on_create</tt>
14 # * (-) <tt>validate</tt>
15 # * (-) <tt>validate_on_create</tt>
16 # * (3) <tt>after_validation</tt>
17 # * (4) <tt>after_validation_on_create</tt>
18 # * (5) <tt>before_save</tt>
19 # * (6) <tt>before_create</tt>
20 # * (-) <tt>create</tt>
21 # * (7) <tt>after_create</tt>
22 # * (8) <tt>after_save</tt>
24 # That's a total of eight callbacks, which gives you immense power to react and prepare for each state in the
25 # Active Record lifecycle. The sequence for calling <tt>Base#save</tt> an existing record is similar, except that each
26 # <tt>_on_create</tt> callback is replaced by the corresponding <tt>_on_update</tt> callback.
29 # class CreditCard < ActiveRecord::Base
30 # # Strip everything but digits, so the user can specify "555 234 34" or
31 # # "5552-3434" or both will mean "55523434"
32 # def before_validation_on_create
33 # self.number = number.gsub(/[^0-9]/, "") if attribute_present?("number")
37 # class Subscription < ActiveRecord::Base
38 # before_create :record_signup
42 # self.signed_up_on = Date.today
46 # class Firm < ActiveRecord::Base
47 # # Destroys the associated clients and people when the firm is destroyed
48 # before_destroy { |record| Person.destroy_all "firm_id = #{record.id}" }
49 # before_destroy { |record| Client.destroy_all "client_of = #{record.id}" }
52 # == Inheritable callback queues
54 # Besides the overwritable callback methods, it's also possible to register callbacks through the use of the callback macros.
55 # Their main advantage is that the macros add behavior into a callback queue that is kept intact down through an inheritance
58 # class Topic < ActiveRecord::Base
59 # before_destroy :destroy_author
63 # before_destroy :destroy_readers
66 # Now, when <tt>Topic#destroy</tt> is run only +destroy_author+ is called. When <tt>Reply#destroy</tt> is run, both +destroy_author+ and
67 # +destroy_readers+ are called. Contrast this to the situation where we've implemented the save behavior through overwriteable
70 # class Topic < ActiveRecord::Base
71 # def before_destroy() destroy_author end
75 # def before_destroy() destroy_readers end
78 # In that case, <tt>Reply#destroy</tt> would only run +destroy_readers+ and _not_ +destroy_author+. So, use the callback macros when
79 # you want to ensure that a certain callback is called for the entire hierarchy, and use the regular overwriteable methods
80 # when you want to leave it up to each descendant to decide whether they want to call +super+ and trigger the inherited callbacks.
82 # *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the callbacks before specifying the
83 # associations. Otherwise, you might trigger the loading of a child before the parent has registered the callbacks and they won't
86 # == Types of callbacks
88 # There are four types of callbacks accepted by the callback macros: Method references (symbol), callback objects,
89 # inline methods (using a proc), and inline eval methods (using a string). Method references and callback objects are the
90 # recommended approaches, inline methods using a proc are sometimes appropriate (such as for creating mix-ins), and inline
91 # eval methods are deprecated.
93 # The method reference callbacks work by specifying a protected or private method available in the object, like this:
95 # class Topic < ActiveRecord::Base
96 # before_destroy :delete_parents
100 # self.class.delete_all "parent_id = #{id}"
104 # The callback objects have methods named after the callback called with the record as the only parameter, such as:
106 # class BankAccount < ActiveRecord::Base
107 # before_save EncryptionWrapper.new
108 # after_save EncryptionWrapper.new
109 # after_initialize EncryptionWrapper.new
112 # class EncryptionWrapper
113 # def before_save(record)
114 # record.credit_card_number = encrypt(record.credit_card_number)
117 # def after_save(record)
118 # record.credit_card_number = decrypt(record.credit_card_number)
121 # alias_method :after_find, :after_save
125 # # Secrecy is committed
129 # # Secrecy is unveiled
133 # So you specify the object you want messaged on a given callback. When that callback is triggered, the object has
134 # a method by the name of the callback messaged. You can make these callbacks more flexible by passing in other
135 # initialization data such as the name of the attribute to work with:
137 # class BankAccount < ActiveRecord::Base
138 # before_save EncryptionWrapper.new("credit_card_number")
139 # after_save EncryptionWrapper.new("credit_card_number")
140 # after_initialize EncryptionWrapper.new("credit_card_number")
143 # class EncryptionWrapper
144 # def initialize(attribute)
145 # @attribute = attribute
148 # def before_save(record)
149 # record.send("#{@attribute}=", encrypt(record.send("#{@attribute}")))
152 # def after_save(record)
153 # record.send("#{@attribute}=", decrypt(record.send("#{@attribute}")))
156 # alias_method :after_find, :after_save
160 # # Secrecy is committed
164 # # Secrecy is unveiled
168 # The callback macros usually accept a symbol for the method they're supposed to run, but you can also pass a "method string",
169 # which will then be evaluated within the binding of the callback. Example:
171 # class Topic < ActiveRecord::Base
172 # before_destroy 'self.class.delete_all "parent_id = #{id}"'
175 # Notice that single quotes (') are used so the <tt>#{id}</tt> part isn't evaluated until the callback is triggered. Also note that these
176 # inline callbacks can be stacked just like the regular ones:
178 # class Topic < ActiveRecord::Base
179 # before_destroy 'self.class.delete_all "parent_id = #{id}"',
180 # 'puts "Evaluated after parents are destroyed"'
183 # == The +after_find+ and +after_initialize+ exceptions
185 # 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
186 # to implement a simple performance constraint (50% more speed on a simple test case). Unlike all the other callbacks, +after_find+ and
187 # +after_initialize+ will only be run if an explicit implementation is defined (<tt>def after_find</tt>). In that case, all of the
188 # callback types will be called.
190 # == <tt>before_validation*</tt> returning statements
192 # 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+.
193 # If Base#save! is called it will raise a ActiveRecord::RecordInvalid exception.
194 # Nothing will be appended to the errors object.
196 # == Canceling callbacks
198 # 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
199 # +false+, all the later callbacks are cancelled. Callbacks are generally run in the order they are defined, with the exception of callbacks
200 # defined as methods on the model, which are called last.
204 # The entire callback chain of a +save+, <tt>save!</tt>, or +destroy+ call runs
205 # within a transaction. That includes <tt>after_*</tt> hooks. If everything
206 # goes fine a COMMIT is executed once the chain has been completed.
208 # If a <tt>before_*</tt> callback cancels the action a ROLLBACK is issued. You
209 # can also trigger a ROLLBACK raising an exception in any of the callbacks,
210 # including <tt>after_*</tt> hooks. Note, however, that in that case the client
211 # needs to be aware of it because an ordinary +save+ will raise such exception
212 # instead of quietly returning +false+.
215 after_find after_initialize before_save after_save before_create after_create before_update after_update before_validation
216 after_validation before_validation_on_create after_validation_on_create before_validation_on_update
217 after_validation_on_update before_destroy after_destroy
220 def self.included(base
) #:nodoc:
221 base
.extend Observable
223 [:create_or_update, :valid?, :create, :update, :destroy].each
do |method
|
224 base
.send
:alias_method_chain, method
, :callbacks
227 base
.send
:include, ActiveSupport
::Callbacks
228 base
.define_callbacks
*CALLBACKS
231 # Is called when the object was instantiated by one of the finders, like <tt>Base.find</tt>.
232 #def after_find() end
234 # Is called after the object has been instantiated by a call to <tt>Base.new</tt>.
235 #def after_initialize() end
237 # Is called _before_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
238 def before_save() end
240 # Is called _after_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
241 # Note that this callback is still wrapped in the transaction around +save+. For example, if you
242 # invoke an external indexer at this point it won't see the changes in the database.
244 # class Contact < ActiveRecord::Base
245 # after_save { logger.info( 'New contact saved!' ) }
248 def create_or_update_with_callbacks
#:nodoc:
249 return false if callback(:before_save) == false
250 if result
= create_or_update_without_callbacks
251 callback(:after_save)
255 private :create_or_update_with_callbacks
257 # Is called _before_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
258 def before_create() end
260 # Is called _after_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
261 # Note that this callback is still wrapped in the transaction around +save+. For example, if you
262 # invoke an external indexer at this point it won't see the changes in the database.
263 def after_create() end
264 def create_with_callbacks
#:nodoc:
265 return false if callback(:before_create) == false
266 result
= create_without_callbacks
267 callback(:after_create)
270 private :create_with_callbacks
272 # Is called _before_ <tt>Base.save</tt> on existing objects that have a record.
273 def before_update() end
275 # Is called _after_ <tt>Base.save</tt> on existing objects that have a record.
276 # Note that this callback is still wrapped in the transaction around +save+. For example, if you
277 # invoke an external indexer at this point it won't see the changes in the database.
278 def after_update() end
280 def update_with_callbacks(*args
) #:nodoc:
281 return false if callback(:before_update) == false
282 result
= update_without_callbacks(*args
)
283 callback(:after_update)
286 private :update_with_callbacks
288 # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
289 def before_validation() end
291 # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
292 def after_validation() end
294 # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
295 # that haven't been saved yet (no record exists).
296 def before_validation_on_create() end
298 # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
299 # that haven't been saved yet (no record exists).
300 def after_validation_on_create() end
302 # Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on
303 # existing objects that have a record.
304 def before_validation_on_update() end
306 # Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on
307 # existing objects that have a record.
308 def after_validation_on_update() end
310 def valid_with_callbacks
? #:nodoc:
311 return false if callback(:before_validation) == false
312 if new_record
? then result
= callback(:before_validation_on_create) else result
= callback(:before_validation_on_update) end
313 return false if false == result
315 result
= valid_without_callbacks
?
317 callback(:after_validation)
318 if new_record
? then callback(:after_validation_on_create) else callback(:after_validation_on_update) end
323 # Is called _before_ <tt>Base.destroy</tt>.
325 # Note: If you need to _destroy_ or _nullify_ associated records first,
326 # use the <tt>:dependent</tt> option on your associations.
327 def before_destroy() end
329 # Is called _after_ <tt>Base.destroy</tt> (and all the attributes have been frozen).
331 # class Contact < ActiveRecord::Base
332 # after_destroy { |record| logger.info( "Contact #{record.id} was destroyed." ) }
334 def after_destroy() end
335 def destroy_with_callbacks
#:nodoc:
336 return false if callback(:before_destroy) == false
337 result
= destroy_without_callbacks
338 callback(:after_destroy)
344 result
= run_callbacks(method
) { |result
, object
| false == result
}
346 if result
!= false && respond_to_without_attributes
?(method
)
347 result
= send(method
)
355 def notify(method
) #:nodoc:
357 self.class.notify_observers(method
, self)