361 lines
15 KiB
Ruby
361 lines
15 KiB
Ruby
require 'observer'
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module ActiveRecord
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# Callbacks are hooks into the lifecycle of an Active Record object that allow you to trigger logic
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# before or after an alteration of the object state. This can be used to make sure that associated and
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# dependent objects are deleted when +destroy+ is called (by overwriting +before_destroy+) or to massage attributes
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# before they're validated (by overwriting +before_validation+). As an example of the callbacks initiated, consider
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# the <tt>Base#save</tt> call for a new record:
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#
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# * (-) <tt>save</tt>
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# * (-) <tt>valid</tt>
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# * (1) <tt>before_validation</tt>
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# * (2) <tt>before_validation_on_create</tt>
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# * (-) <tt>validate</tt>
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# * (-) <tt>validate_on_create</tt>
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# * (3) <tt>after_validation</tt>
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# * (4) <tt>after_validation_on_create</tt>
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# * (5) <tt>before_save</tt>
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# * (6) <tt>before_create</tt>
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# * (-) <tt>create</tt>
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# * (7) <tt>after_create</tt>
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# * (8) <tt>after_save</tt>
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#
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# That's a total of eight callbacks, which gives you immense power to react and prepare for each state in the
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# Active Record lifecycle. The sequence for calling <tt>Base#save</tt> an existing record is similar, except that each
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# <tt>_on_create</tt> callback is replaced by the corresponding <tt>_on_update</tt> callback.
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#
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# Examples:
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# class CreditCard < ActiveRecord::Base
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# # Strip everything but digits, so the user can specify "555 234 34" or
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# # "5552-3434" or both will mean "55523434"
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# def before_validation_on_create
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# self.number = number.gsub(/[^0-9]/, "") if attribute_present?("number")
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# end
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# end
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#
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# class Subscription < ActiveRecord::Base
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# before_create :record_signup
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#
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# private
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# def record_signup
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# self.signed_up_on = Date.today
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# end
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# end
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#
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# class Firm < ActiveRecord::Base
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# # Destroys the associated clients and people when the firm is destroyed
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# before_destroy { |record| Person.destroy_all "firm_id = #{record.id}" }
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# before_destroy { |record| Client.destroy_all "client_of = #{record.id}" }
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# end
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#
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# == Inheritable callback queues
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#
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# Besides the overwritable callback methods, it's also possible to register callbacks through the use of the callback macros.
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# Their main advantage is that the macros add behavior into a callback queue that is kept intact down through an inheritance
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# hierarchy. Example:
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#
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# class Topic < ActiveRecord::Base
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# before_destroy :destroy_author
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# end
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#
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# class Reply < Topic
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# before_destroy :destroy_readers
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# end
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#
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# Now, when <tt>Topic#destroy</tt> is run only +destroy_author+ is called. When <tt>Reply#destroy</tt> is run, both +destroy_author+ and
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# +destroy_readers+ are called. Contrast this to the situation where we've implemented the save behavior through overwriteable
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# methods:
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#
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# class Topic < ActiveRecord::Base
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# def before_destroy() destroy_author end
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# end
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#
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# class Reply < Topic
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# def before_destroy() destroy_readers end
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# end
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#
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# In that case, <tt>Reply#destroy</tt> would only run +destroy_readers+ and _not_ +destroy_author+. So, use the callback macros when
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# you want to ensure that a certain callback is called for the entire hierarchy, and use the regular overwriteable methods
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# when you want to leave it up to each descendant to decide whether they want to call +super+ and trigger the inherited callbacks.
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#
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# *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the callbacks before specifying the
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# associations. Otherwise, you might trigger the loading of a child before the parent has registered the callbacks and they won't
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# be inherited.
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#
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# == Types of callbacks
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#
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# There are four types of callbacks accepted by the callback macros: Method references (symbol), callback objects,
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# inline methods (using a proc), and inline eval methods (using a string). Method references and callback objects are the
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# recommended approaches, inline methods using a proc are sometimes appropriate (such as for creating mix-ins), and inline
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# eval methods are deprecated.
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#
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# The method reference callbacks work by specifying a protected or private method available in the object, like this:
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#
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# class Topic < ActiveRecord::Base
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# before_destroy :delete_parents
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#
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# private
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# def delete_parents
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# self.class.delete_all "parent_id = #{id}"
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# end
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# end
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#
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# The callback objects have methods named after the callback called with the record as the only parameter, such as:
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#
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# class BankAccount < ActiveRecord::Base
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# before_save EncryptionWrapper.new
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# after_save EncryptionWrapper.new
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# after_initialize EncryptionWrapper.new
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# end
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#
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# class EncryptionWrapper
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# def before_save(record)
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# record.credit_card_number = encrypt(record.credit_card_number)
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# end
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#
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# def after_save(record)
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# record.credit_card_number = decrypt(record.credit_card_number)
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# end
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#
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# alias_method :after_find, :after_save
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#
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# private
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# def encrypt(value)
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# # Secrecy is committed
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# end
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#
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# def decrypt(value)
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# # Secrecy is unveiled
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# end
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# end
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#
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# So you specify the object you want messaged on a given callback. When that callback is triggered, the object has
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# a method by the name of the callback messaged. You can make these callbacks more flexible by passing in other
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# initialization data such as the name of the attribute to work with:
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#
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# class BankAccount < ActiveRecord::Base
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# before_save EncryptionWrapper.new("credit_card_number")
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# after_save EncryptionWrapper.new("credit_card_number")
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# after_initialize EncryptionWrapper.new("credit_card_number")
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# end
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#
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# class EncryptionWrapper
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# def initialize(attribute)
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# @attribute = attribute
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# end
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#
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# def before_save(record)
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# record.send("#{@attribute}=", encrypt(record.send("#{@attribute}")))
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# end
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#
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# def after_save(record)
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# record.send("#{@attribute}=", decrypt(record.send("#{@attribute}")))
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# end
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#
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# alias_method :after_find, :after_save
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#
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# private
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# def encrypt(value)
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# # Secrecy is committed
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# end
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#
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# def decrypt(value)
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# # Secrecy is unveiled
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# end
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# end
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#
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# The callback macros usually accept a symbol for the method they're supposed to run, but you can also pass a "method string",
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# which will then be evaluated within the binding of the callback. Example:
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#
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# class Topic < ActiveRecord::Base
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# before_destroy 'self.class.delete_all "parent_id = #{id}"'
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# end
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#
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# Notice that single quotes (') are used so the <tt>#{id}</tt> part isn't evaluated until the callback is triggered. Also note that these
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# inline callbacks can be stacked just like the regular ones:
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#
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# class Topic < ActiveRecord::Base
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# before_destroy 'self.class.delete_all "parent_id = #{id}"',
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# 'puts "Evaluated after parents are destroyed"'
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# end
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#
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# == The +after_find+ and +after_initialize+ exceptions
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#
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# 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
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# to implement a simple performance constraint (50% more speed on a simple test case). Unlike all the other callbacks, +after_find+ and
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# +after_initialize+ will only be run if an explicit implementation is defined (<tt>def after_find</tt>). In that case, all of the
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# callback types will be called.
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#
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# == <tt>before_validation*</tt> returning statements
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#
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# 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+.
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# If Base#save! is called it will raise a ActiveRecord::RecordInvalid exception.
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# Nothing will be appended to the errors object.
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#
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# == Canceling callbacks
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#
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# 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
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# +false+, all the later callbacks are cancelled. Callbacks are generally run in the order they are defined, with the exception of callbacks
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# defined as methods on the model, which are called last.
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#
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# == Transactions
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#
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# The entire callback chain of a +save+, <tt>save!</tt>, or +destroy+ call runs
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# within a transaction. That includes <tt>after_*</tt> hooks. If everything
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# goes fine a COMMIT is executed once the chain has been completed.
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#
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# If a <tt>before_*</tt> callback cancels the action a ROLLBACK is issued. You
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# can also trigger a ROLLBACK raising an exception in any of the callbacks,
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# including <tt>after_*</tt> hooks. Note, however, that in that case the client
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# needs to be aware of it because an ordinary +save+ will raise such exception
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# instead of quietly returning +false+.
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module Callbacks
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CALLBACKS = %w(
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after_find after_initialize before_save after_save before_create after_create before_update after_update before_validation
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after_validation before_validation_on_create after_validation_on_create before_validation_on_update
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after_validation_on_update before_destroy after_destroy
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)
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def self.included(base) #:nodoc:
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base.extend Observable
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[:create_or_update, :valid?, :create, :update, :destroy].each do |method|
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base.send :alias_method_chain, method, :callbacks
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end
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base.send :include, ActiveSupport::Callbacks
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base.define_callbacks *CALLBACKS
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end
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# Is called when the object was instantiated by one of the finders, like <tt>Base.find</tt>.
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#def after_find() end
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# Is called after the object has been instantiated by a call to <tt>Base.new</tt>.
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#def after_initialize() end
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# Is called _before_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
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def before_save() end
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# Is called _after_ <tt>Base.save</tt> (regardless of whether it's a +create+ or +update+ save).
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# Note that this callback is still wrapped in the transaction around +save+. For example, if you
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# invoke an external indexer at this point it won't see the changes in the database.
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#
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# class Contact < ActiveRecord::Base
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# after_save { logger.info( 'New contact saved!' ) }
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# end
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def after_save() end
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def create_or_update_with_callbacks #:nodoc:
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return false if callback(:before_save) == false
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if result = create_or_update_without_callbacks
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callback(:after_save)
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end
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result
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end
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private :create_or_update_with_callbacks
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# Is called _before_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
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def before_create() end
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# Is called _after_ <tt>Base.save</tt> on new objects that haven't been saved yet (no record exists).
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# Note that this callback is still wrapped in the transaction around +save+. For example, if you
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# invoke an external indexer at this point it won't see the changes in the database.
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def after_create() end
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def create_with_callbacks #:nodoc:
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return false if callback(:before_create) == false
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result = create_without_callbacks
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callback(:after_create)
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result
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end
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private :create_with_callbacks
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# Is called _before_ <tt>Base.save</tt> on existing objects that have a record.
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def before_update() end
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# Is called _after_ <tt>Base.save</tt> on existing objects that have a record.
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# Note that this callback is still wrapped in the transaction around +save+. For example, if you
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# invoke an external indexer at this point it won't see the changes in the database.
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def after_update() end
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def update_with_callbacks(*args) #:nodoc:
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return false if callback(:before_update) == false
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result = update_without_callbacks(*args)
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callback(:after_update)
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result
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end
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private :update_with_callbacks
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# Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
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def before_validation() end
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# Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call).
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def after_validation() end
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# Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
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# that haven't been saved yet (no record exists).
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def before_validation_on_create() end
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# Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on new objects
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# that haven't been saved yet (no record exists).
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def after_validation_on_create() end
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# Is called _before_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on
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# existing objects that have a record.
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def before_validation_on_update() end
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# Is called _after_ <tt>Validations.validate</tt> (which is part of the <tt>Base.save</tt> call) on
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# existing objects that have a record.
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def after_validation_on_update() end
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def valid_with_callbacks? #:nodoc:
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return false if callback(:before_validation) == false
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if new_record? then result = callback(:before_validation_on_create) else result = callback(:before_validation_on_update) end
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return false if false == result
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result = valid_without_callbacks?
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callback(:after_validation)
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if new_record? then callback(:after_validation_on_create) else callback(:after_validation_on_update) end
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return result
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end
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# Is called _before_ <tt>Base.destroy</tt>.
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#
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# Note: If you need to _destroy_ or _nullify_ associated records first,
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# use the <tt>:dependent</tt> option on your associations.
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def before_destroy() end
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# Is called _after_ <tt>Base.destroy</tt> (and all the attributes have been frozen).
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#
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# class Contact < ActiveRecord::Base
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# after_destroy { |record| logger.info( "Contact #{record.id} was destroyed." ) }
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# end
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def after_destroy() end
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def destroy_with_callbacks #:nodoc:
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return false if callback(:before_destroy) == false
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result = destroy_without_callbacks
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callback(:after_destroy)
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result
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end
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private
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def callback(method)
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result = run_callbacks(method) { |result, object| false == result }
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if result != false && respond_to_without_attributes?(method)
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result = send(method)
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end
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notify(method)
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return result
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end
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def notify(method) #:nodoc:
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self.class.changed
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self.class.notify_observers(method, self)
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end
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end
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end
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