Rails: includes with polymorphic association

I read this interesting article about Using Polymorphism to Make a Better Activity Feed in Rails. We end up with something like ``` class Activity < ActiveRecord::Base belongs_to :subject, polymorphic: true end ``` Now, if two of those subjects are for example: ``` class Event < ActiveRecord::Base has_many :guests after_create :create_activities has_one :activity, as: :subject, dependent: :destroy end class Image < ActiveRecord::Base has_many :tags after_create :create_activities has_one :activity, as: :subject, dependent: :destroy end ``` With create_activities defined as ``` def create_activities Activity.create(subject: self) end ``` And with guests and tags defined as: ``` class Guest < ActiveRecord::Base belongs_to :event end class Tag < ActiveRecord::Base belongs_to :image end ``` If we query the last 20 activities logged, we can do: ``` Activity.order(created_at: :desc).limit(20) ``` We have a first N+1 query issue that we can solve with: ``` Activity.includes(:subject).order(created_at: :desc).limit(20) ``` But then, when we call guests or tags, we have another N+1 query problem. What's the proper way to solve that in order to be able to use pagination ?