# module ActiveSupport::Callbacks::ClassMethods

### Public Instance Methods

__callback_runner_name(key, kind) click to toggle source

    # File lib/active_support/callbacks.rb, line 413
    def __callback_runner_name(key, kind)
      "_run__#{self.name.hash.abs}__#{kind}__#{key.hash.abs}__callbacks"
    end

__reset_runner(symbol) click to toggle source

    # File lib/active_support/callbacks.rb, line 408
    def __reset_runner(symbol)
      name = __callback_runner_name(nil, symbol)
      undef_method(name) if method_defined?(name)
    end

define_callbacks(*callbacks) click to toggle source

Define sets of events in the object lifecycle 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 is a string to be eval’ed. The result of the callback is available in the `result` variable.

      define_callbacks :validate, :terminator => "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.

- `:rescuable` - By default, after filters are not executed if the given block or a before filter raises an error. By setting this option to `true` exception raised by given block is stored and after executing all the after callbacks the stored exception is raised.

- `: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`.

    # File lib/active_support/callbacks.rb, line 616
    def define_callbacks(*callbacks)
      config = callbacks.last.is_a?(Hash) ? callbacks.pop : {}
      callbacks.each do |callback|
        class_attribute "_#{callback}_callbacks"
        send("_#{callback}_callbacks=", CallbackChain.new(callback, config))
        __define_runner(callback)
      end
    end

reset_callbacks(symbol) click to toggle source

Remove all set callbacks for the given event.

    # File lib/active_support/callbacks.rb, line 535
    def reset_callbacks(symbol)
      callbacks = send("_#{symbol}_callbacks")

      ActiveSupport::DescendantsTracker.descendants(self).each do |target|
        chain = target.send("_#{symbol}_callbacks").dup
        callbacks.each { |c| chain.delete(c) }
        target.send("_#{symbol}_callbacks=", chain)
        target.__reset_runner(symbol)
      end

      self.send("_#{symbol}_callbacks=", callbacks.dup.clear)

      __reset_runner(symbol)
    end

set_callback(name, *filter_list, &block) click to toggle source

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, lambda { |r| stuff; result = yield; 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 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_callback`.

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.

- `:per_key` - A hash with `:if` and `:unless` options; see “Per-key conditions” below.

##### Per-key conditions

When creating or skipping callbacks, you can specify conditions that are always the same for a given key. For instance, in Action Pack, we convert :only and :except conditions into per-key conditions.

    before_filter :authenticate, :except => "index"

becomes

    set_callback :process_action, :before, :authenticate, :per_key => {:unless => proc {|c| c.action_name == "index"}}

Per-key conditions are evaluated only once per use of a given key. In the case of the above example, you would do:

    run_callbacks(:process_action, action_name) { ... dispatch stuff ... }

In that case, each action_name would get its own compiled callback method that took into consideration the per_key conditions. This is a speed improvement for ActionPack.

    # File lib/active_support/callbacks.rb, line 491
    def set_callback(name, *filter_list, &block)
      mapped = nil

      __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
        mapped ||= filters.map do |filter|
          Callback.new(chain, filter, type, options.dup, self)
        end

        filters.each do |filter|
          chain.delete_if {|c| c.matches?(type, filter) }
        end

        options[:prepend] ? chain.unshift(*(mapped.reverse)) : chain.push(*mapped)

        target.send("_#{name}_callbacks=", chain)
      end
    end

skip_callback(name, *filter_list, &block) click to toggle source

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 => lambda { self.age > 18 }
    end

    # File lib/active_support/callbacks.rb, line 516
    def skip_callback(name, *filter_list, &block)
      __update_callbacks(name, filter_list, block) do |target, chain, type, filters, options|
        filters.each do |filter|
          filter = chain.find {|c| c.matches?(type, filter) }

          if filter && options.any?
            new_filter = filter.clone(chain, self)
            chain.insert(chain.index(filter), new_filter)
            new_filter.recompile!(options, options[:per_key] || {})
          end

          chain.delete(filter)
        end
        target.send("_#{name}_callbacks=", chain)
      end
    end