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July 9, 2018 05:48
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# frozen_string_literal: true | |
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.encrypted[: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 | |
current_instances[name] ||= new | |
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_value(&:reset) | |
end | |
def clear_all # :nodoc: | |
reset_all | |
current_instances.clear | |
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 |
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