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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
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Included Modules

Attributes

[RW] attributes

Class Public methods

after_reset(*methods, &block)

Alias for: resets

attribute(*names, default: nil)

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 112
def attribute(*names, default: nil)
  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

  Delegation.generate(singleton_class, names, to: :instance, nilable: false, signature: "")
  Delegation.generate(singleton_class, names.map { |n| "#{n}=" }, to: :instance, nilable: false, signature: "value")

  self.defaults = defaults.merge(names.index_with { default })
end

before_reset(*methods, &block)

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

# File activesupport/lib/active_support/current_attributes.rb, line 142
def before_reset(*methods, &block)
  set_callback :reset, :before, *methods, &block
end

instance()

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

# File activesupport/lib/active_support/current_attributes.rb, line 100
def instance
  current_instances[current_instances_key] ||= new
end

new()

# File activesupport/lib/active_support/current_attributes.rb, line 196
def initialize
  @attributes = resolve_defaults
end

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
# File activesupport/lib/active_support/current_attributes.rb, line 147
def resets(*methods, &block)
  set_callback :reset, :after, *methods, &block
end

Instance Public methods

reset()

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

# File activesupport/lib/active_support/current_attributes.rb, line 215
def reset
  run_callbacks :reset do
    self.attributes = resolve_defaults
  end
end

set(attributes, &block)

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
# File activesupport/lib/active_support/current_attributes.rb, line 210
def set(attributes, &block)
  with(**attributes, &block)
end