[rom-sql] AR-like polymorphic associations (PLEASE DON'T USE IT UNLESS YOU HAVE A LEGACY SCHEMA)

rom-sql-ar-like-polymorphic-associations.rb

require 'rom-repository'
require 'rom-sql'
require 'logger'

config = ROM::Configuration.new(:sql, 'sqlite::memory')

config.gateways[:default].connection.create_table(:songs) do
  primary_key :id
  column :title, String
end

config.gateways[:default].connection.create_table(:books) do
  primary_key :id
  column :title, String
end

config.gateways[:default].connection.create_table(:tags) do
  primary_key :id
  column :taggable_id, Integer
  column :taggable_type, String
  column :name, String
end

config.relation(:songs) do
  schema(infer: true) do
    associations do
      has_many :tags, foreign_key: :taggable_id, view: :for_songs
    end
  end

  def for_tags(tags)
    by_pk(tags.select { |tag| tag[:taggable_type] == 'Song' }.map { |tag| tag[:taggable_id] })
  end
end

config.relation(:books) do
  schema(infer: true) do
    associations do
      has_many :tags, foreign_key: :taggable_id, view: :for_books
    end
  end

  def for_tags(tags)
    by_pk(tags.select { |tag| tag[:taggable_type] == 'Book' }.map { |tag| tag[:taggable_id] })
  end
end

config.relation(:tags) do
  schema(infer: true) do
    associations do
      belongs_to :books, as: :book, foreign_key: :taggable_id, view: :for_tags
      belongs_to :songs, as: :song, foreign_key: :taggable_id, view: :for_tags
    end
  end

  def for_songs
    where(taggable_type: 'Song')
  end

  def for_books
    where(taggable_type: 'Book')
  end
end

class SongRepo < ROM::Repository[:songs]
  relations :tags
  commands :create
end

class BookRepo < ROM::Repository[:books]
  relations :tags
  commands :create
end

class TagRepo < ROM::Repository[:tags]
  relations :songs, :books
  commands :create
end

rom = ROM.container(config)

song_repo = SongRepo.new(rom)
book_repo = BookRepo.new(rom)
tag_repo = TagRepo.new(rom)

song = song_repo.create(title: 'A song')
book = book_repo.create(title: 'A book')

song_tag = tag_repo.create(taggable_id: song.id, taggable_type: 'Song', name: 'red')
book_tag = tag_repo.create(taggable_id: book.id, taggable_type: 'Book', name: 'blue')

puts song_repo.aggregate(:tags).to_a.first.inspect
#<ROM::Struct[Song] id=1 title="A song" tags=[#<ROM::Struct[Tag] id=1 taggable_id=1 taggable_type="Song" name="red">]>

puts book_repo.aggregate(:tags).to_a.first.inspect
#<ROM::Struct[Book] id=1 title="A book" tags=[#<ROM::Struct[Tag] id=2 taggable_id=1 taggable_type="Book" name="blue">]>

puts tag_repo.tags.wrap(:book).for_books.to_a.first.inspect
# #<ROM::Struct[Tag] id=2 taggable_id=1 taggable_type="Book" name="blue" book=#<ROM::Struct[Book] id=1 title="A book">>

puts tag_repo.tags.wrap(:song).for_songs.to_a.first.inspect
# #<ROM::Struct[Tag] id=1 taggable_id=1 taggable_type="Song" name="red" song=#<ROM::Struct[Song] id=1 title="A song">>