Module: ActiveSupport::Callbacks::ClassMethods

### Home Classes Methods

### In Files

- lib/active_support/callbacks.rb

### Methods

- #define_callbacks
- #reset_callbacks
- #set_callback
- #skip_callback

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# ActiveSupport::Callbacks::ClassMethods

### Public Instance Methods

define_callbacks(*callbacks) click to toggle source

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 lib/active_support/callbacks.rb, line 589
    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

reset_callbacks(symbol) click to toggle source

Reset callbacks for a given type.

    # File lib/active_support/callbacks.rb, line 514
    def reset_callbacks(symbol)
      callbacks = send("_#{symbol}_callbacks")

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

      callbacks.clear
      __define_runner(symbol)
    end

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

Set callbacks for a previously defined callback.

Syntax:

    set_callback :save, :before, :before_meth
    set_callback :save, :after,  :after_meth, :if => :condition
    set_callback :save, :around, lambda { |r| stuff; yield; stuff }

Use skip_callback to skip any defined one.

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

    dispatch_callback :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(:dispatch, 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 478
    def set_callback(name, *filter_list, &block)
      mapped = nil

      __update_callbacks(name, filter_list, block) do |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)
      end
    end

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

Skip a previously defined callback for a given type.

    # File lib/active_support/callbacks.rb, line 496
    def skip_callback(name, *filter_list, &block)
      __update_callbacks(name, filter_list, block) do |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
      end
    end

[Validate]

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