Module: ActiveSupport::Callbacks::ClassMethods

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

Instance Method Summary collapse

Instance Method Details

#__update_callbacks(name) ⇒ Object

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



620
621
622
623
624
625
 
# File 'activesupport/lib/active_support/callbacks.rb', line 620

def __update_callbacks(name) #:nodoc:
  ([self] + ActiveSupport::DescendantsTracker.descendants(self)).reverse_each do |target|
    chain = target.get_callbacks name
    yield target, chain.dup
  end
end

#define_callbacks(*names) ⇒ Object

Define sets of events in the object life cycle 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 before and around callbacks from being called and the event from being triggered. This should be a lambda to be executed. The current object and the result lambda of the callback will be provided to the terminator lambda.

    define_callbacks :validate, terminator: ->(target, result_lambda) { result_lambda.call == false }

    In this example, if any before validate callbacks returns false, any successive before and around callback is not executed.

    The default terminator halts the chain when a callback throws :abort.

  • :skip_after_callbacks_if_terminated - Determines if after callbacks should be terminated by the :terminator option. By default after callbacks are executed no matter if callback chain was terminated or not. This option has no effect if :terminator option is set to nil.

  • :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.

Notes

names passed to define_callbacks must not end with !, ? or =.

Calling define_callbacks multiple times with the same names will overwrite previous callbacks registered with set_callback.



810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
 
# File 'activesupport/lib/active_support/callbacks.rb', line 810

def define_callbacks(*names)
  options = names.extract_options!

  names.each do |name|
    name = name.to_sym

    ([self] + ActiveSupport::DescendantsTracker.descendants(self)).each do |target|
      target.set_callbacks name, CallbackChain.new(name, options)
    end

    module_eval <<-RUBY, __FILE__, __LINE__ + 1
      def _run_#{name}_callbacks(&block)
        run_callbacks #{name.inspect}, &block
      end

      def self._#{name}_callbacks
        get_callbacks(#{name.inspect})
      end

      def self._#{name}_callbacks=(value)
        set_callbacks(#{name.inspect}, value)
      end

      def _#{name}_callbacks
        __callbacks[#{name.inspect}]
      end
    RUBY
  end
end

#normalize_callback_params(filters, block) ⇒ Object

:nodoc:



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

def normalize_callback_params(filters, block) # :nodoc:
  type = CALLBACK_FILTER_TYPES.include?(filters.first) ? filters.shift : :before
  options = filters.extract_options!
  filters.unshift(block) if block
  [type, filters, options.dup]
end

#reset_callbacks(name) ⇒ Object

Remove all set callbacks for the given event.



720
721
722
723
724
725
726
727
728
729
730
 
# File 'activesupport/lib/active_support/callbacks.rb', line 720

def reset_callbacks(name)
  callbacks = get_callbacks name

  ActiveSupport::DescendantsTracker.descendants(self).each do |target|
    chain = target.get_callbacks(name).dup
    callbacks.each { |c| chain.delete(c) }
    target.set_callbacks name, chain
  end

  set_callbacks(name, callbacks.dup.clear)
end

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

Install a callback for the given event.

set_callback :save, :before, :before_method
set_callback :save, :after,  :after_method, if: :condition
set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }

The second argument 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_method

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

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 or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a true value.

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

  • :unless - A symbol or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a false value.

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

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



671
672
673
674
675
676
677
678
679
680
681
682
683
 
# File 'activesupport/lib/active_support/callbacks.rb', line 671

def set_callback(name, *filter_list, &block)
  type, filters, options = normalize_callback_params(filter_list, block)

  self_chain = get_callbacks name
  mapped = filters.map do |filter|
    Callback.build(self_chain, filter, type, options)
  end

  __update_callbacks(name) do |target, chain|
    options[:prepend] ? chain.prepend(*mapped) : chain.append(*mapped)
    target.set_callbacks name, 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: -> { age > 18 }
end

An ArgumentError will be raised if the callback has not already been set (unless the :raise option is set to false).



695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
 
# File 'activesupport/lib/active_support/callbacks.rb', line 695

def skip_callback(name, *filter_list, &block)
  type, filters, options = normalize_callback_params(filter_list, block)

  options[:raise] = true unless options.key?(:raise)

  __update_callbacks(name) do |target, chain|
    filters.each do |filter|
      callback = chain.find { |c| c.matches?(type, filter) }

      if !callback && options[:raise]
        raise ArgumentError, "#{type.to_s.capitalize} #{name} callback #{filter.inspect} has not been defined"
      end

      if callback && (options.key?(:if) || options.key?(:unless))
        new_callback = callback.merge_conditional_options(chain, if_option: options[:if], unless_option: options[:unless])
        chain.insert(chain.index(callback), new_callback)
      end

      chain.delete(callback)
    end
    target.set_callbacks name, chain
  end
end