Rails: has_many distinct through: source: の習作 https://note.com/usutani/n/n741bd5112e43

has_many__distinct__through__source.rb

# frozen_string_literal: true

# Rails: 私の好きなコード（5）永続化とロジックを絶妙にブレンドするActive Record（翻訳）
# https://techracho.bpsinc.jp/hachi8833/2023_04_18/127103
# Topic
#   has_many :entry_creators, -> { distinct }, through: :entries, source: :creator
#
# https://github.com/rails/rails/blob/main/guides/bug_report_templates/active_record_gem.rb
# Rename: Post(posts) => Topic(topics), Comment(comments) => Entry(entries)
# New: Creator(creators)

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "~> 7.0.0"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :topics, force: true do |t|
  end
  create_table :entries, force: true do |t|
    t.integer :topic_id
    t.integer :creator_id
  end
  create_table :creators, force: true do |t|
  end
end

class Topic < ActiveRecord::Base
  has_many :entries
  has_many :entry_creators, -> { distinct }, through: :entries, source: :creator
end
class Entry < ActiveRecord::Base
  belongs_to :topic
  belongs_to :creator
end
class Creator < ActiveRecord::Base
  has_many :entries
end

class BugTest < Minitest::Test
  def test_association_stuff
    topic = Topic.create!
    creator = Creator.create!
    Entry.create! topic: topic, creator: creator
    Entry.create! topic: topic, creator: creator

    assert_equal 2, topic.entries.count
    assert_equal 1, topic.entry_creators.count
  end
end