Rails: share information within a Request scope

Question

What's the mechanism in Rails to share information within the current request scope?

Those familiar with Asp.Net would know there is a HttpContext that is available to all the entities that are invoked during a request.

Anything similar in Rails?

Answer 1

With around_filter and Thread.current[] you can easily create a request context/scope. See the following example.

First add in your application_controller.rb:

  around_filter :request_context

  def request_context
    begin
      RequestContext.begin_request
      yield
    ensure
      RequestContext.end_request
    end
  end

now add the following class to lib/request_context.rb

class RequestContext
  def self.instance
    i = Thread.current[:request_context]
    unless i
      raise "No instance present. In script/rakefiles: use RequestContext.with_scope {}, " +
            "in controller: ensure `around_filter :request_scope` is configured"
    end
    return i
  end

  # Allows the use of this scope from rake/scripts
  # ContextScope.with_scope do |scope|
  #   # do something
  #   ...
  # end
  def self.with_scope
    begin
      begin_request
      yield(instance)
    ensure
      end_request
    end
  end

  def self.begin_request
    raise "request_context already set" if Thread.current[:request_context]
    Thread.current[:request_context] = RequestContext.new
  end

  def self.end_request
    raise "request_context already nil" unless Thread.current[:request_context]
    Thread.current[:request_context] = nil
  end

  # user part, add constructors/getters/setters here

  def initialize
    # you can setup stuff here, be aware that this
    # is being called in _every_ request.
  end
end

This is pretty straightforward. You can store data in the RequestContext.instance object, the object will get recreated after every request.