Callbacks are code hooks that are run at key points in an object’s lifecycle. 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 lifecycle 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).
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.
Example
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
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. Optionally accepts a key, which will be used to compile an optimized callback method for each key. See ClassMethods.define_callbacks for more information.
If the callback chain was halted, returns false. Otherwise returns the result of the block, or true if no block is given.
run_callbacks :save do
save
end