define_callbacks

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 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.

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.