Module: ActiveSupport::Callbacks::ClassMethods

Defined in:
activesupport/lib/active_support/callbacks.rb

Instance Method Summary collapse

Instance Method Details

#__create_keyed_callback(name, kind, object, &blk) ⇒ Object

This is called the first time a callback is called with a particular key. It creates a new callback method for the key, calculating which callbacks can be omitted because of per_key conditions.



400
401
402
403
404
405
406
407
408
409
410
# File 'activesupport/lib/active_support/callbacks.rb', line 400

def __create_keyed_callback(name, kind, object, &blk) #:nodoc:
  @_keyed_callbacks ||= {}
  @_keyed_callbacks[name] ||= begin
    str = send("_#{kind}_callbacks").compile(name, object)
    class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
      def #{name}() #{str} end
      protected :#{name}
    RUBY_EVAL
    true
  end
end

#__define_runner(symbol) ⇒ Object

Generate the internal runner method called by run_callbacks.



372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
# File 'activesupport/lib/active_support/callbacks.rb', line 372

def __define_runner(symbol) #:nodoc:
  body = send("_#{symbol}_callbacks").compile

  silence_warnings do
    undef_method "_run_#{symbol}_callbacks" if method_defined?("_run_#{symbol}_callbacks")
    class_eval <<-RUBY_EVAL, __FILE__, __LINE__ + 1
      def _run_#{symbol}_callbacks(key = nil, &blk)
        if key
          name = "_run__\#{self.class.name.hash.abs}__#{symbol}__\#{key.hash.abs}__callbacks"

          unless respond_to?(name)
            self.class.__create_keyed_callback(name, :#{symbol}, self, &blk)
          end

          send(name, &blk)
        else
          #{body}
        end
      end
      private :_run_#{symbol}_callbacks
    RUBY_EVAL
  end
end

#__update_callbacks(name, filters = [], block = nil) ⇒ Object

This is used internally to append, prepend and skip callbacks to the CallbackChain.



415
416
417
418
419
420
421
422
423
424
425
# File 'activesupport/lib/active_support/callbacks.rb', line 415

def __update_callbacks(name, filters = [], block = nil) #:nodoc:
  type = filters.first.in?([:before, :after, :around]) ? filters.shift : :before
  options = filters.last.is_a?(Hash) ? filters.pop : {}
  filters.unshift(block) if block

  ([self] + ActiveSupport::DescendantsTracker.descendants(self)).reverse.each do |target|
    chain = target.send("_#{name}_callbacks")
    yield target, chain.dup, type, filters, options
    target.__define_runner(name)
  end
end

#define_callbacks(*callbacks) ⇒ Object

Define sets of events in the object lifecycle that support callbacks.

define_callbacks :validate
define_callbacks :initialize, :save, :destroy
Options
  • :terminator - Determines when a before filter will halt the callback chain, preventing following callbacks from being called and the event from being triggered. This is a string to be eval'ed. The result of the callback is available in the result variable.

    define_callbacks :validate, :terminator => "result == false"
    

    In this example, if any before validate callbacks returns false, other callbacks are not executed. Defaults to “false”, meaning no value halts the chain.

  • :rescuable - By default, after filters are not executed if the given block or a before filter raises an error. By setting this option to true exception raised by given block is stored and after executing all the after callbacks the stored exception is raised.

  • :scope - Indicates which methods should be executed when an object is used as a callback.

    class Audit
      def before(caller)
        puts 'Audit: before is called'
      end
    
      def before_save(caller)
        puts 'Audit: before_save is called'
      end
    end
    
    class Account
      include ActiveSupport::Callbacks
    
      define_callbacks :save
      set_callback :save, :before, Audit.new
    
      def save
        run_callbacks :save do
          puts 'save in main'
        end
      end
    end
    

    In the above case whenever you save an account the method Audit#before will be called. On the other hand

    define_callbacks :save, :scope => [:kind, :name]
    

    would trigger Audit#before_save instead. That's constructed by calling #{kind}_#{name} on the given instance. In this case “kind” is “before” and “name” is “save”. In this context :kind and :name have special meanings: :kind refers to the kind of callback (before/after/around) and :name refers to the method on which callbacks are being defined.

    A declaration like

    define_callbacks :save, :scope => [:name]
    

    would call Audit#save.



611
612
613
614
615
616
617
618
# File 'activesupport/lib/active_support/callbacks.rb', line 611

def define_callbacks(*callbacks)
  config = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
  callbacks.each do |callback|
    class_attribute "_#{callback}_callbacks"
    send("_#{callback}_callbacks=", CallbackChain.new(callback, config))
    __define_runner(callback)
  end
end

#reset_callbacks(symbol) ⇒ Object

Remove all set callbacks for the given event.



530
531
532
533
534
535
536
537
538
539
540
541
542
543
# File 'activesupport/lib/active_support/callbacks.rb', line 530

def reset_callbacks(symbol)
  callbacks = send("_#{symbol}_callbacks")

  ActiveSupport::DescendantsTracker.descendants(self).each do |target|
    chain = target.send("_#{symbol}_callbacks").dup
    callbacks.each { |c| chain.delete(c) }
    target.send("_#{symbol}_callbacks=", chain)
    target.__define_runner(symbol)
  end

  self.send("_#{symbol}_callbacks=", callbacks.dup.clear)

  __define_runner(symbol)
end

#set_callback(name, *filter_list, &block) ⇒ Object

Install a callback for the given event.

set_callback :save, :before, :before_meth
set_callback :save, :after,  :after_meth, :if => :condition
set_callback :save, :around, lambda { |r| stuff; result = yield; stuff }

The second arguments indicates whether the callback is to be run :before, :after, or :around the event. If omitted, :before is assumed. This means the first example above can also be written as:

set_callback :save, :before_meth

The callback can specified as a symbol naming an instance method; as a proc, lambda, or block; as a string to be instance evaluated; or as an object that responds to a certain method determined by the :scope argument to define_callback.

If a proc, lambda, or block is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.

Before and around callbacks are called in the order that they are set; after callbacks are called in the reverse order.

Around callbacks can access the return value from the event, if it wasn't halted, from the yield call.

Options
  • :if - A symbol naming an instance method or a proc; the callback will be called only when it returns a true value.

  • :unless - A symbol naming an instance method or a proc; the callback will be called only when it returns a false value.

  • :prepend - If true, the callback will be prepended to the existing chain rather than appended.

  • :per_key - A hash with :if and :unless options; see “Per-key conditions” below.

Per-key conditions

When creating or skipping callbacks, you can specify conditions that are always the same for a given key. For instance, in Action Pack, we convert :only and :except conditions into per-key conditions.

before_filter :authenticate, :except => "index"

becomes

set_callback :process_action, :before, :authenticate, :per_key => {:unless => proc {|c| c.action_name == "index"}}

Per-key conditions are evaluated only once per use of a given key. In the case of the above example, you would do:

run_callbacks(:process_action, action_name) { ... dispatch stuff ... }

In that case, each action_name would get its own compiled callback method that took into consideration the per_key conditions. This is a speed improvement for ActionPack.



486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
# File 'activesupport/lib/active_support/callbacks.rb', line 486

def set_callback(name, *filter_list, &block)
  mapped = nil

  __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
    mapped ||= filters.map do |filter|
      Callback.new(chain, filter, type, options.dup, self)
    end

    filters.each do |filter|
      chain.delete_if {|c| c.matches?(type, filter) }
    end

    options[:prepend] ? chain.unshift(*(mapped.reverse)) : chain.push(*mapped)

    target.send("_#{name}_callbacks=", chain)
  end
end

#skip_callback(name, *filter_list, &block) ⇒ Object

Skip a previously set callback. Like set_callback, :if or :unless options may be passed in order to control when the callback is skipped.

class Writer < Person
   skip_callback :validate, :before, :check_membership, :if => lambda { self.age > 18 }
end


511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
# File 'activesupport/lib/active_support/callbacks.rb', line 511

def skip_callback(name, *filter_list, &block)
  __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
    filters.each do |filter|
      filter = chain.find {|c| c.matches?(type, filter) }

      if filter && options.any?
        new_filter = filter.clone(chain, self)
        chain.insert(chain.index(filter), new_filter)
        new_filter.recompile!(options, options[:per_key] || {})
      end

      chain.delete(filter)
    end
    target.send("_#{name}_callbacks=", chain)
  end
end