module ActiveSupport
# Abstract super class that provides a thread-isolated attributes singleton, which resets automatically
# before and after each request. This allows you to keep all the per-request attributes easily
# available to the whole system.
#
# The following full app-like example demonstrates how to use a Current class to
# facilitate easy access to the global, per-request attributes without passing them deeply
# around everywhere:
#
# # app/models/current.rb
# class Current < ActiveSupport::CurrentAttributes
# attribute :account, :user
# attribute :request_id, :user_agent, :ip_address
#
# resets { Time.zone = nil }
#
# def user=(user)
# super
# self.account = user.account
# Time.zone = user.time_zone
# end
# end
#
# # app/controllers/concerns/authentication.rb
# module Authentication
# extend ActiveSupport::Concern
#
# included do
# before_action :authenticate
# end
#
# private
# def authenticate
# if authenticated_user = User.find_by(id: cookies.signed[:user_id])
# Current.user = authenticated_user
# else
# redirect_to new_session_url
# end
# end
# end
#
# # app/controllers/concerns/set_current_request_details.rb
# module SetCurrentRequestDetails
# extend ActiveSupport::Concern
#
# included do
# before_action do
# Current.request_id = request.uuid
# Current.user_agent = request.user_agent
# Current.ip_address = request.ip
# end
# end
# end
#
# class ApplicationController < ActionController::Base
# include Authentication
# include SetCurrentRequestDetails
# end
#
# class MessagesController < ApplicationController
# def create
# Current.account.messages.create(message_params)
# end
# end
#
# class Message < ApplicationRecord
# belongs_to :creator, default: -> { Current.user }
# after_create { |message| Event.create(record: message) }
# end
#
# class Event < ApplicationRecord
# before_create do
# self.request_id = Current.request_id
# self.user_agent = Current.user_agent
# self.ip_address = Current.ip_address
# end
# end
#
# A word of caution: It's easy to overdo a global singleton like Current and tangle your model as a result.
# Current should only be used for a few, top-level globals, like account, user, and request details.
# The attributes stuck in Current should be used by more or less all actions on all requests. If you start
# sticking controller-specific attributes in there, you're going to create a mess.
class CurrentAttributes
include ActiveSupport::Callbacks
define_callbacks :reset
class << self
# Returns singleton instance for this class in this thread. If none exists, one is created.
def instance
Thread.current[:"current_attributes_for_#{name}"] ||= new.tap do |instance|
current_instances << instance
end
end
# Declares one or more attributes that will be given both class and instance accessor methods.
def attribute(*names)
generated_attribute_methods.module_eval do
names.each do |name|
define_method(name) do
attributes[name.to_sym]
end
define_method("#{name}=") do |attribute|
attributes[name.to_sym] = attribute
end
end
end
names.each do |name|
define_singleton_method(name) do
instance.public_send(name)
end
define_singleton_method("#{name}=") do |attribute|
instance.public_send("#{name}=", attribute)
end
end
end
# Calls this block after #reset is called on the instance. Used for resetting external collaborators, like Time.zone.
def resets(&block)
set_callback :reset, :after, &block
end
delegate :set, :reset, to: :instance
def reset_all # :nodoc:
current_instances.each(&:reset)
end
private
def generated_attribute_methods
@generated_attribute_methods ||= Module.new.tap { |mod| include mod }
end
def current_instances
Thread.current[:current_attributes_instances] ||= []
end
def method_missing(name, *args, &block)
# Caches the method definition as a singleton method of the receiver.
#
# By letting #delegate handle it, we avoid an enclosure that'll capture args.
singleton_class.delegate name, to: :instance
send(name, *args, &block)
end
end
attr_accessor :attributes
def initialize
@attributes = {}
end
# Expose one or more attributes within a block. Old values are returned after the block concludes.
# Example demonstrating the common use of needing to set Current attributes outside the request-cycle:
#
# class Chat::PublicationJob < ApplicationJob
# def perform(attributes, room_number, creator)
# Current.set(person: creator) do
# Chat::Publisher.publish(attributes: attributes, room_number: room_number)
# end
# end
# end
def set(set_attributes)
old_attributes = compute_attributes(set_attributes.keys)
assign_attributes(set_attributes)
yield
ensure
assign_attributes(old_attributes)
end
# Reset all attributes. Should be called before and after actions, when used as a per-request singleton.
def reset
run_callbacks :reset do
self.attributes = {}
end
end
private
def assign_attributes(new_attributes)
new_attributes.each { |key, value| public_send("#{key}=", value) }
end
def compute_attributes(keys)
keys.collect { |key| [ key, public_send(key) ] }.to_h
end
end
end
