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
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
saving... - save saved
# File activesupport/lib/active_support/callbacks.rb, line 94 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 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 && skipped.first break env.value end end # 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.call end end end
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
© 2004–2018 David Heinemeier Hansson
Licensed under the MIT License.