define_callbacks

Defines callbacks types:

define_callbacks :validate

This macro accepts the following options:

• :terminator - Indicates when a before filter is considered

to be halted.

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

In the example above, 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. Set this option to true to change this behavior.

• :scope - Indicates which methods should be executed when a class

is given as callback. Defaults to [:kind].

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.

# File activesupport/lib/active_support/callbacks.rb, line 590
      def define_callbacks(*callbacks)
        config = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
        callbacks.each do |callback|
          extlib_inheritable_reader("_#{callback}_callbacks") do
            CallbackChain.new(callback, config)
          end
          __define_runner(callback)
        end
      end