Module: ActiveSupport::Callbacks::ClassMethods

Relationships & Source Files
Defined in:	activesupport/lib/active_support/callbacks.rb

Instance Method Summary

#define_callbacks(*names)

Define sets of events in the object life cycle that support callbacks.
#reset_callbacks(name)

Remove all set callbacks for the given event.
#set_callback(name, *filter_list, &block)

Install a callback for the given event.
#skip_callback(name, *filter_list, &block)

Skip a previously set callback.

Instance Method Details

#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 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, other callbacks are 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 =.

[ GitHub ]

# File 'activesupport/lib/active_support/callbacks.rb', line 769


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

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

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

#reset_callbacks(name)

Remove all set callbacks for the given event.

[ GitHub ]

# File 'activesupport/lib/active_support/callbacks.rb', line 686


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, a string or an array of symbols and strings, each naming an instance method or a proc; the callback will be called only when they all return a true value.
:unless - A symbol, a string or an array of symbols and strings, each naming an instance method or a proc; the callback will be called only when they all return a false value.
:prepend - If true, the callback will be prepended to the existing chain rather than appended.

[ GitHub ]

# File 'activesupport/lib/active_support/callbacks.rb', line 647


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

[ GitHub ]

# File 'activesupport/lib/active_support/callbacks.rb', line 667


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