How to avoid n+1 queries when using polymorphic associations?

Question

I have 4 models, let's say:

class Photo < ActiveRecord::Base
  belongs_to :photoable, polymorphic: true
end

class User < ActiveRecord::Base
  has_one :photo, as: :photoable
end    

class Company < ActiveRecord::Base
  has_one :photo, as: :photoable
  has_many :products
end

class Products < ActiveRecord::Base
  belongs_to :company
end

So, the query Photo.all.includes(:photoable) works.

But if I use Photo.all.includes(photoable: :products) only works if all loaded photos belongs to Company. If the relation contains photos of users and companies, this error is raised:

ActiveRecord::ConfigurationError (Association named 'products' was not found; perhaps you misspelled it?):

This occurs because user hasn't relationship with products.

Is there any way to eager load users and companies with products for a relation of photos?

EDIT:

This question isn't duplicated of Eager load polymorphic. As I commented below, in this question I want to do eager load for polymorphic associations which has different associations(one has products and the other don't). In that question, the OP uses wrong names for table names.

Answer 1

You may add specific associations to Photo model:

class Photo < ActiveRecord::Base
  belongs_to :photoable, polymorphic: true

  belongs_to :user, -> { where(photoable_type: 'User' ) }, foreign_key: :photoable_id
  belongs_to :company, -> { where(photoable_type: 'Company' ) }, foreign_key: :photoable_id
end

After that you may preload nested specific associations:

photos = Photo.all.includes(:photoable, company: :products)

With access to records like this:

photos.each do |photo|
  puts photo.photoable.inspect
  puts photo.company.products.inspect if photo.photoable_type == "Company"
end

This approach loads company association twice, but does not do n+1 queries.