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 has no effect if:terminator
option is set tonil
. -
: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 handdefine_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
.
# File activesupport/lib/active_support/callbacks.rb, line 813 def define_callbacks(*names) options = names.extract_options! names.each do |name| name = name.to_sym ([self] + ActiveSupport::DescendantsTracker.descendants(self)).each do |target| target.set_callbacks name, CallbackChain.new(name, options) end module_eval <<-RUBY, __FILE__, __LINE__ + 1 def _run_#{name}_callbacks(&block) run_callbacks #{name.inspect}, &block end def self._#{name}_callbacks get_callbacks(#{name.inspect}) end def self._#{name}_callbacks=(value) set_callbacks(#{name.inspect}, value) end def _#{name}_callbacks __callbacks[#{name.inspect}] end RUBY end end
Remove all set callbacks for the given event.
# File activesupport/lib/active_support/callbacks.rb, line 723 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 set_callbacks(name, callbacks.dup.clear) end
Install a callback for the given event.
set_callback :save, :before, :before_method
set_callback :save, :after, :after_method, if: :condition
set_callback :save, :around, ->(r, block) { stuff; result = block.call; stuff }
The second argument 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_method
The callback can be specified as a symbol naming an instance method; as a proc, lambda, or block; 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 or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a true value.If a proc is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.
-
:unless
- A symbol or an array of symbols, each naming an instance method or a proc; the callback will be called only when they all return a false value.If a proc is given, its body is evaluated in the context of the current object. It can also optionally accept the current object as an argument.
-
:prepend
- Iftrue
, the callback will be prepended to the existing chain rather than appended.
# File activesupport/lib/active_support/callbacks.rb, line 674 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 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: -> { age > 18 }
end
An ArgumentError
will be raised if the callback has not already been set (unless the :raise
option is set to false
).
# File activesupport/lib/active_support/callbacks.rb, line 698 def skip_callback(name, *filter_list, &block) type, filters, options = normalize_callback_params(filter_list, block) options[:raise] = true unless options.key?(:raise) __update_callbacks(name) do |target, chain| filters.each do |filter| callback = chain.find { |c| c.matches?(type, filter) } if !callback && options[:raise] raise ArgumentError, "#{type.to_s.capitalize} #{name} callback #{filter.inspect} has not been defined" end if callback && (options.key?(:if) || options.key?(:unless)) new_callback = callback.merge_conditional_options(chain, if_option: options[:if], unless_option: options[:unless]) chain.insert(chain.index(callback), new_callback) end chain.delete(callback) end target.set_callbacks name, chain end end