Rails polymorphic HABTM relation

polymorphic_HABTM_relation.rb

# The problem: I needed to create bundles, to be able to sell collections of both courses as well as tracks. (and in the future possibly more things)
# But in return, a track/course can also belong to multiple bundles.
# So: bundle has_many tracks/courses, tracks/courses has_many bundles
# (This was work in progress, but if I remember correctly, it works.)

# app/models/bundle.rb
class Bundle < ActiveRecord::Base
  # Creating a polymorphic HABTM relation in Rails is not possible,
  # this does basically the same thing
  has_many :bundles_bundleables # terrible naming
  has_many :tracks, through: :bundles_bundleables, source: :bundleable, source_type: 'Track'
  has_many :courses, through: :bundles_bundleables, source: :bundleable, source_type: 'Course'
  ...
end

# app/models/bundles_bundleable.rb
class BundlesBundleable < ActiveRecord::Base
  belongs_to :bundle
  belongs_to :bundleable, :polymorphic => true
end

# app/models/track.rb
class Track < ActiveRecord::Base
  has_many :bundles_bundleables, as: :bundleable
  has_many :bundles, through: :bundles_bundleables
  ...
end

# Same for course.rb as for track.