1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
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
|
