Sometimes you need preload associations, not join, separate load. And with this method you can preload on arrays too!

gistfile1.rb

class ApplicationController < ActiionController::Base
  def preload_associations(*associations)
    collection = get_collection_ivar
    associations.each do |association|
      ActiveRecord::Associations::Preloader.new(collection, association).run
    end
    set_collection_ivar collection
    collection
  end
end

class SomeControllerInTheWild < ApplicationController
  def index
    bla bla bla
    preload_associations(:posts, shops: [:comments])
end