Current Attributes¶ ↑
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.
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Attributes
[W] | attributes |
Class Public methods
attribute(*names, default: NOT_SET) Link
Declares one or more attributes that will be given both class and instance accessor methods.
Options¶ ↑
-
:default
- The default value for the attributes. If the value is a proc or lambda, it will be called whenever an instance is constructed. Otherwise, the value will be duplicated with dup. Default values are re-assigned when the attributes are reset.
# File activesupport/lib/active_support/current_attributes.rb, line 115 def attribute(*names, default: NOT_SET) invalid_attribute_names = names.map(&:to_sym) & INVALID_ATTRIBUTE_NAMES if invalid_attribute_names.any? raise ArgumentError, "Restricted attribute names: #{invalid_attribute_names.join(", ")}" end Delegation.generate(singleton_class, names, to: :instance, nilable: false, signature: "") Delegation.generate(singleton_class, names.map { |n| "#{n}=" }, to: :instance, nilable: false, signature: "value") ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |owner| names.each do |name| owner.define_cached_method(name, namespace: :current_attributes) do |batch| batch << "def #{name}" << "@attributes[:#{name}]" << "end" end owner.define_cached_method("#{name}=", namespace: :current_attributes) do |batch| batch << "def #{name}=(value)" << "@attributes[:#{name}] = value" << "end" end end end self.defaults = defaults.merge(names.index_with { default }) end
before_reset(*methods, &block) Link
Calls this callback before reset
is called on the instance. Used for resetting external collaborators that depend on current values.
instance() Link
Returns singleton instance for this class in this thread. If none exists, one is created.
new() Link
resets(*methods, &block) Link
Calls this callback after reset
is called on the instance. Used for resetting external collaborators, like Time.zone
.
Instance Public methods
attributes() Link
reset() Link
Reset all attributes. Should be called before and after actions, when used as a per-request singleton.
set(attributes, &block) Link
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