Concerns, Decorators, Presenters, Service Objects, Helpers - Help me Understand Them [closed]

Answer 1

Concerns

Are used to share functionality between files in one 'type' ('model', 'controller', ...). Thus you have

  /app
    /controllers
       /concerns

    /models
       /concerns

In concerns you put modules which will be included inside classes. It is god practice to put some behaviour code. For example

/app
  /models
    /concerns
       messageable.rb
    project.rb
    ..
    proposal.rb

Project model

class Project < ActiveRecord::Base
  include Messageable
end

Proposal model

class Proposal < ActiveRecord::Base
  include Messageable
end

inside app/models/concerns/messageable.rb

require 'active_record/concern'
module Messageable
  extend ActiveSupport::Concern

  # implement behaviour
  module ClassMethods
     # class methods for the behaviour
  end
end