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Methods
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Instance Public methods
define_callbacks(*names)

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 return result of the callback will be called with the lambda.

    define_callbacks :validate, terminator: ->(target, result) { result == false }
    

    In this example, if any before validate callbacks returns false, any successive before and around callback is not executed. Defaults to false, meaning no value halts the chain.

  • :skip_after_callbacks_if_terminated - Determines if after callbacks should be terminated by the :terminator option. By default after callbacks executed no matter if callback chain was terminated or not. Option makes sense only when :terminator option is specified.

  • :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.

NOTE: method_name passed to `define_model_callbacks` must not end with `!`, `?` or `=`.

# File activesupport/lib/active_support/callbacks.rb, line 726
      def define_callbacks(*names)
        options = names.extract_options!

        names.each do |name|
          class_attribute "_#{name}_callbacks"
          set_callbacks name, CallbackChain.new(name, options)

          module_eval "            def _run_#{name}_callbacks(&block)
              _run_callbacks(_#{name}_callbacks, &block)
            end
", __FILE__, __LINE__ + 1
        end
      end
reset_callbacks(name)

Remove all set callbacks for the given event.

# File activesupport/lib/active_support/callbacks.rb, line 642
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

  self.set_callbacks name, callbacks.dup.clear
end
set_callback(name, *filter_list, &block)

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, ->(r, block) { stuff; result = block.call; 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 be 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_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 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.

# File activesupport/lib/active_support/callbacks.rb, line 603
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)

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: -> { self.age > 18 }
end
# File activesupport/lib/active_support/callbacks.rb, line 623
def skip_callback(name, *filter_list, &block)
  type, filters, options = normalize_callback_params(filter_list, block)

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

      if filter && options.any?
        new_filter = filter.merge(chain, options)
        chain.insert(chain.index(filter), new_filter)
      end

      chain.delete(filter)
    end
    target.set_callbacks name, chain
  end
end
Instance Protected methods
get_callbacks(name)
# File activesupport/lib/active_support/callbacks.rb, line 743
def get_callbacks(name)
  send "_#{name}_callbacks"
end
set_callbacks(name, callbacks)
# File activesupport/lib/active_support/callbacks.rb, line 747
def set_callbacks(name, callbacks)
  send "_#{name}_callbacks=", callbacks
end