Callbacks
are code hooks that are run at key points in an object's life cycle. The typical use case is to have a base class define a set of callbacks relevant to the other functionality it supplies, so that subclasses can install callbacks that enhance or modify the base functionality without needing to override or redefine methods of the base class.
Mixing in this module allows you to define the events in the object's life cycle that will support callbacks (via ClassMethods#define_callbacks
), set the instance methods, procs, or callback objects to be called (via ClassMethods#set_callback
), and run the installed callbacks at the appropriate times (via run_callbacks
).
By default callbacks are halted by throwing :abort
. See ClassMethods#define_callbacks
for details.
Three kinds of callbacks are supported: before callbacks, run before a certain event; after callbacks, run after the event; and around callbacks, blocks that surround the event, triggering it when they yield. Callback code can be contained in instance methods, procs or lambdas, or callback objects that respond to certain predetermined methods. See ClassMethods#set_callback
for details.
class Record
include ActiveSupport::Callbacks
define_callbacks :save
def save
run_callbacks :save do
puts "- save"
end
end
end
class PersonRecord < Record
set_callback :save, :before, :saving_message
def saving_message
puts "saving..."
end
set_callback :save, :after do |object|
puts "saved"
end
end
person = PersonRecord.new
person.save
Output:
saving...
- save
saved
- MODULE ActiveSupport::Callbacks::CallTemplate
- MODULE ActiveSupport::Callbacks::ClassMethods
- MODULE ActiveSupport::Callbacks::Conditionals
- MODULE ActiveSupport::Callbacks::Filters
Constants
CALLBACK_FILTER_TYPES | = | [:before, :after, :around] |
Instance Public methods
run_callbacks(kind) Link
Runs the callbacks for the given event.
Calls the before and around callbacks in the order they were set, yields the block (if given one), and then runs the after callbacks in reverse order.
If the callback chain was halted, returns false
. Otherwise returns the result of the block, nil
if no callbacks have been set, or true
if callbacks have been set but no block is given.
run_callbacks :save do
save
end
# File activesupport/lib/active_support/callbacks.rb, line 95 def run_callbacks(kind) callbacks = __callbacks[kind.to_sym] if callbacks.empty? yield if block_given? else env = Filters::Environment.new(self, false, nil) next_sequence = callbacks.compile # Common case: no 'around' callbacks defined if next_sequence.final? next_sequence.invoke_before(env) env.value = !env.halted && (!block_given? || yield) next_sequence.invoke_after(env) env.value else invoke_sequence = Proc.new do skipped = nil while true current = next_sequence current.invoke_before(env) if current.final? env.value = !env.halted && (!block_given? || yield) elsif current.skip?(env) (skipped ||= []) << current next_sequence = next_sequence.nested next else next_sequence = next_sequence.nested begin target, block, method, *arguments = current.expand_call_template(env, invoke_sequence) target.send(method, *arguments, &block) ensure next_sequence = current end end current.invoke_after(env) skipped.pop.invoke_after(env) while skipped&.first break env.value end end invoke_sequence.call end end end