sidekiq_indexing.rb

module SidekiqIndexing
  module SearchableOverride
    extend ActiveSupport::Concern

    module InstanceOverrides
      def solr_index
        SunspotIndexer.perform_async(self.class.to_s, self.id)
      end
    end

    module ClassMethods
      def searchable(*args, &blk)
        super
        include InstanceOverrides
      end
    end
  end

  class Railtie < ::Rails::Railtie
    initializer 'sidekiq_indexing.init' do
      ActiveSupport.on_load(:active_record) do
        include(SidekiqIndexing::SearchableOverride)
      end
    end
  end
end

sunspot_indexer.rb

class SunspotIndexer
  include Sidekiq::Worker

  def perform(klass_name, id)
    Sunspot.index(klass_name.constantize.find(id))
  end
end