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Diffstat (limited to 'activesupport/lib/active_support/current_attributes.rb')
| -rw-r--r-- | activesupport/lib/active_support/current_attributes.rb | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/current_attributes.rb b/activesupport/lib/active_support/current_attributes.rb new file mode 100644 index 0000000000..3145ff87a1 --- /dev/null +++ b/activesupport/lib/active_support/current_attributes.rb @@ -0,0 +1,197 @@ +# frozen_string_literal: true + +require "active_support/callbacks" + +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 |