85 lines
2.8 KiB
Ruby
85 lines
2.8 KiB
Ruby
require 'singleton'
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module ActiveRecord
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# Observer classes respond to lifecycle callbacks to implement trigger-like
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# behavior outside the original class. This is a great way to reduce the
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# clutter that normally comes when the model class is burdened with
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# functionality that doesn't pertain to the core responsibility of the
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# class. Example:
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#
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# class CommentObserver < ActiveRecord::Observer
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# def after_save(comment)
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# Notifications.deliver_comment("admin@do.com", "New comment was posted", comment)
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# end
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# end
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#
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# This Observer sends an email when a Comment#save is finished.
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#
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# == Observing a class that can't be inferred
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#
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# Observers will by default be mapped to the class with which they share a name. So CommentObserver will
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# be tied to observing Comment, ProductManagerObserver to ProductManager, and so on. If you want to name your observer
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# differently than the class you're interested in observing, you can use the Observer.observe class method:
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#
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# class AuditObserver < ActiveRecord::Observer
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# observe Account
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#
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# def after_update(account)
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# AuditTrail.new(account, "UPDATED")
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# end
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# end
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#
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# If the audit observer needs to watch more than one kind of object, this can be specified with multiple arguments:
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#
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# class AuditObserver < ActiveRecord::Observer
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# observe Account, Balance
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#
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# def after_update(record)
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# AuditTrail.new(record, "UPDATED")
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# end
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# end
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#
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# The AuditObserver will now act on both updates to Account and Balance by treating them both as records.
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#
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# == Available callback methods
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#
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# The observer can implement callback methods for each of the methods described in the Callbacks module.
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#
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# == Triggering Observers
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#
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# In order to activate an observer, you need to call Observer.instance. In Rails, this can be done in controllers
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# using the short-hand of for example observer :comment_observer.
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class Observer
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include Singleton
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# Attaches the observer to the supplied model classes.
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def self.observe(*models)
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define_method(:observed_class) { models }
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end
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def initialize
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[ observed_class ].flatten.each do |klass|
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klass.add_observer(self)
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klass.send(:define_method, :after_find) unless klass.respond_to?(:after_find)
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end
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end
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def update(callback_method, object) #:nodoc:
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send(callback_method, object) if respond_to?(callback_method)
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end
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private
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def observed_class
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if self.class.respond_to? "observed_class"
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self.class.observed_class
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else
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Object.const_get(infer_observed_class_name)
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end
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end
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def infer_observed_class_name
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self.class.name.scan(/(.*)Observer/)[0][0]
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end
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end
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end
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