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.

Methods

Included Modules

Attributes

[RW] attributes

Class Public methods

after_reset(*methods, &block)

Alias for: resets

attribute(*names)

Declares one or more attributes that will be given both class and instance accessor methods.

📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 104
      def attribute(*names)
        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

        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

        ActiveSupport::CodeGenerator.batch(singleton_class, __FILE__, __LINE__) do |owner|
          names.each do |name|
            owner.define_cached_method(name, namespace: :current_attributes_delegation) do |batch|
              batch <<
                "def #{name}" <<
                "instance.#{name}" <<
                "end"
            end
            owner.define_cached_method("#{name}=", namespace: :current_attributes_delegation) do |batch|
              batch <<
                "def #{name}=(value)" <<
                "instance.#{name} = value" <<
                "end"
            end
          end
        end
      end
🔎 See on GitHub

before_reset(*methods, &block)

Calls this callback before reset is called on the instance. Used for resetting external collaborators that depend on current values.

📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 146
      def before_reset(*methods, &block)
        set_callback :reset, :before, *methods, &block
      end
🔎 See on GitHub

instance()

Returns singleton instance for this class in this thread. If none exists, one is created.

📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 99
      def instance
        current_instances[current_instances_key] ||= new
      end
🔎 See on GitHub

new()

📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 197
    def initialize
      @attributes = {}
    end
🔎 See on GitHub

resets(*methods, &block)

Calls this callback after reset is called on the instance. Used for resetting external collaborators, like Time.zone.

Also aliased as: after_reset
📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 151
      def resets(*methods, &block)
        set_callback :reset, :after, *methods, &block
      end
🔎 See on GitHub

Instance Public methods

reset()

Reset all attributes. Should be called before and after actions, when used as a per-request singleton.

📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 220
    def reset
      run_callbacks :reset do
        self.attributes = {}
      end
    end
🔎 See on GitHub

set(set_attributes)

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
📝 Source code 
# File activesupport/lib/active_support/current_attributes.rb, line 211
    def set(set_attributes)
      old_attributes = compute_attributes(set_attributes.keys)
      assign_attributes(set_attributes)
      yield
    ensure
      assign_attributes(old_attributes)
    end
🔎 See on GitHub