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275 lines
11 KiB
Ruby
275 lines
11 KiB
Ruby
require 'active_support/core_ext/array/wrap'
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module ActiveRecord
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# = Active Record Callbacks
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#
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# Callbacks are hooks into the life cycle 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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# * (-) <tt>validate</tt>
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# * (2) <tt>after_validation</tt>
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# * (3) <tt>before_save</tt>
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# * (4) <tt>before_create</tt>
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# * (-) <tt>create</tt>
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# * (5) <tt>after_create</tt>
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# * (6) <tt>after_save</tt>
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# * (7) <tt>after_commit</tt>
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#
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# Also, an <tt>after_rollback</tt> callback can be configured to be triggered whenever a rollback is issued.
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# Check out <tt>ActiveRecord::Transactions</tt> for more details about <tt>after_commit</tt> and
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# <tt>after_rollback</tt>.
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#
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# Lastly an <tt>after_find</tt> and <tt>after_initialize</tt> callback is triggered for each object that
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# is found and instantiated by a finder, with <tt>after_initialize</tt> being triggered after new objects
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# are instantiated as well.
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#
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# That's a total of twelve callbacks, which gives you immense power to react and prepare for each state in the
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# Active Record life cycle. The sequence for calling <tt>Base#save</tt> for an existing record is similar,
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# except that each <tt>_create</tt> callback is replaced by the corresponding <tt>_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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# before_validation(:on => :create) do
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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
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# use of the callback macros. Their main advantage is that the macros add behavior into a callback
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# queue that is kept intact down through an inheritance hierarchy.
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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
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# run, both +destroy_author+ and +destroy_readers+ are called. Contrast this to the following situation
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# where the +before_destroy+ method is overridden:
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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+.
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# So, use the callback macros when you want to ensure that a certain callback is called for the entire
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# hierarchy, and use the regular overwriteable methods when you want to leave it up to each descendant
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# 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
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# callbacks before specifying the associations. Otherwise, you might trigger the loading of a
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# child before the parent has registered the callbacks and they won't 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
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# are the recommended approaches, inline methods using a proc are sometimes appropriate (such as for
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# creating mix-ins), and inline 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
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# pass a "method string", 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
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# is triggered. Also note that these 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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# == <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
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# aborted and <tt>Base#save</tt> will return +false+. If Base#save! is called it will raise a
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# ActiveRecord::RecordInvalid exception. 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
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# cancelled. If an <tt>after_*</tt> callback returns +false+, all the later callbacks are cancelled.
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# Callbacks are generally run in the order they are defined, with the exception of callbacks defined as
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# 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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#
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# == Debugging callbacks
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#
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# The callback chain is accessible via the <tt>_*_callbacks</tt> method on an object. ActiveModel Callbacks support
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# <tt>:before</tt>, <tt>:after</tt> and <tt>:around</tt> as values for the <tt>kind</tt> property. The <tt>kind</tt> property
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# defines what part of the chain the callback runs in.
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#
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# To find all callbacks in the before_save callback chain:
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#
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# Topic._save_callbacks.select { |cb| cb.kind.eql?(:before) }
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#
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# Returns an array of callback objects that form the before_save chain.
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#
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# To further check if the before_save chain contains a proc defined as <tt>rest_when_dead</tt> use the <tt>filter</tt> property of the callback object:
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#
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# Topic._save_callbacks.select { |cb| cb.kind.eql?(:before) }.collect(&:filter).include?(:rest_when_dead)
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#
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# Returns true or false depending on whether the proc is contained in the before_save callback chain on a Topic model.
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#
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module Callbacks
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extend ActiveSupport::Concern
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CALLBACKS = [
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:after_initialize, :after_find, :after_touch, :before_validation, :after_validation,
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:before_save, :around_save, :after_save, :before_create, :around_create,
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:after_create, :before_update, :around_update, :after_update,
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:before_destroy, :around_destroy, :after_destroy, :after_commit, :after_rollback
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]
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included do
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extend ActiveModel::Callbacks
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include ActiveModel::Validations::Callbacks
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define_model_callbacks :initialize, :find, :touch, :only => :after
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define_model_callbacks :save, :create, :update, :destroy
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end
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def destroy #:nodoc:
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run_callbacks(:destroy) { super }
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end
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def touch(*) #:nodoc:
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run_callbacks(:touch) { super }
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end
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private
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def create_or_update #:nodoc:
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run_callbacks(:save) { super }
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end
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def create #:nodoc:
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run_callbacks(:create) { super }
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end
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def update(*) #:nodoc:
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run_callbacks(:update) { super }
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end
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end
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end
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