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

Does this lead to duplicative, but reversed records on ContentRelationship Or ambiguity on direction?

e.g. Video#5 and Article#41 are related to eachother:

#<ContentRelationship origin_id: 5, origin_type: 'Video', related_content_id: 41, related_content_type: 'Article' >

#<ContentRelationship origin_id: 41, origin_type: 'Article', related_content_id: 5, related_content_type: 'Video' >

Both of these records would be necessary to allow you to traverse both directions, right?

Video.find(5).related_content only works if the first ContentRelationship record exists
Article.find(41).related_content only works if the second ContentRelationship record exists

These rely on performing the JOIN only on the origin column, but SQL allows for AND and OR on joins. I just don't think Rails provides a way to define multiple sources in a has_many

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