Double-polymorphic has_many through modeling in Rails

gistfile1.rb

class Article < ActiveRecord::Base
  has_many :content_relationships, as: :origin, dependent: :destroy

  has_many :related_articles, through: :content_relationships, source: :related_content, source_type: "Article"
  has_many :related_videos,   through: :content_relationships, source: :related_content, source_type: "Video"
end

class Video < ActiveRecord::Base
  has_many :content_relationships, as: :origin, dependent: :destroy

  has_many :related_articles, through: :content_relationships, source: :related_content, source_type: "Article"
  has_many :related_videos,   through: :content_relationships, source: :related_content, source_type: "Video"
end

class ContentRelationship < ActiveRecord::Base
  belongs_to :origin, polymorphic: true
  belongs_to :related_content, polymorphic: true
end

Sorry to say, I have no idea. What you said sounds plausible, though. Note, this gist is 10 years old!