Introducing Concerns

What are Concerns?

Concerns are just modules which allow us to group similar behaviours in one place.

Concerns in controller specifically can be used to share code between controller and also extracting similar behaviours (eg. concerns for SSO, authentication etc.) from controllers for future re-use or for greater clarity and modularity.

Where are Concerns located?

How do you write a concern?

It's pretty simple to write a concern

Create a module under 'concerns' folder
extend the module with ' ActiveSupport::Concern'
Define all the methods which you need to group
include the concern inside your controller, all the methods will be accessible as instance methods now

Example (RequestServiceLoader)

java_import com.bibliocommons.v2.service.request.RequestServicer
 
module RequestServiceLoader
  extend ActiveSupport::Concern
 
  # Allowing to read the request service instead of an instance method
  attr_reader :request_service
 
  def load_services
    setup_request_service
    load_global_service
  end

  def setup_request_service
    @request_service = RequestServicer.new()
    @request_service.enter_request_scope(request.remote_ip, cookies[:agency_id], cookies[:session_id] || params[:session_id], cookies[:language],cookies[:current_scope_id])
  end

 
  .....
end

Example - Adding it to ApplicationController

 class ApplicationController < ActionController::Base
   # We include the module here
   include RequestServiceLoader
 
   # Now we can call the methods directly of RequestServiceLoader
   before_filter :load_services
   
   def some_method 
     # We are using method instead of instance method
     user = request_service.authService.get_logged_in_
   end

 end

obfuscation or common concern?

One thing we can also do in concerns is call filters eg.

 module RequestServiceLoader
   extend ActiveSupport::Concern
   
   included do
     before_filter :load_services
     after_filter  :end_request
  end
  
  def load_services
    ..
  end
  
  def end_request
    ...
  end
end

These filters will be added as soon as you include the module so they may run before your application filters. I think we should avoid it for greater clarity and control.