Rails 的 CurrentAttributes
简介
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.
不使用 CurrentAttributes
def process_data
processor = DataProcessor.new
if processor.call_long_data_processing
processor.log("#{Current.user} called data processing")
end
end
def irrelevant_action
render plain: 'hello'
end
如果 A 用户先访问处理比较慢的 process_data action，然后 B 用户请求了处理很快的 irrelevant_action action。假设，我们的服务器是单线程的，那就没啥问题，只能等 A 用户的请求返回结果之后，才会处理 B 用户的请求。
但如果我们是多线程服务，正好有空余的线程可以处理 B 用户的请求，那么 Current.user 就有可能被改变。
正确使用 CurrentAttributes
# 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
注意事项
- 像
Current这样的全局单例类如果太多，会使得 model 很混乱。 Current应该只被用来处理少数的顶级全局变量，例如account, user和 request details。因为所有请求的所有操作都或多或少的用得上这些属性。- 绝对不要把 controller 专用的属性放在这里。
这里还有一个反向的观点，认为引入了类似全局变量的东西，会增加 Rails 项目代码的理解复杂度，详见 Rails’ CurrentAttributes considered harmful
