Trailblazer Session

The Session

The application can behave differently based on the request URL by presenting a diferent 'site' experience to the end-user, who may also choose from the locales (language presentations) that the site supports.The Session manages this: it's a PORO plus some Trailblazer operations. It keeps state for the current request including current user, the Rails session and site and locale selections. It's established with a Session::Create operation before processing a request.

The Session does not persist across requests, except for data placed in its persistent store, for which the Rails session is used (but another Hash-like object could be used instead).

The Session is established in the ApplicationController:

  before_action do
    Session::Create.reject(params.merge(store: session, host: request.host,           
      preferred_locales: get_preferred_locales_from_http_request)) do |op|
      redirect_to '/404.html'
    end 
  end

The additional parameters that the Session requires are merged into the params hash. If the requested site isn't recognised then a 404 is returned. Note the use of reject instead of run to invert the purpose of the block.

The actual Session is just a PORO with some class instance variables that the Session::Create operation initialises; its state is indeterminate before this is done (note: it may leak from a prior request if not initialised!). It is essentially like this:

class Session
  class << self
    attr_reader :site
    attr_reader :user
    attr_reader :store
  end

The Session::Create operation is like this:

  class Create < Trailblazer::Operation
    def process(params)
      Session.store = params[:store]
      select_site(params[:host]) &&
      select_locale(params[:locale], params[:preferred_locales])
      Session.user = User.find_by_id(Session.store[:user_id])
    end

Private methods do the setup work and return invalid! if they wish to invalidate the session (e.g. unrecognised site)

johnlane/session.md

The Session