ActiveRecord::HasOneAssociationPolymorphicThroughError:

has_one_polymorphic_association.rb

# frozen_string_literal: true

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", "6.0.0"
  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 :hardbacks, force: true do |t|
  end

  create_table :paperbacks, force: true do |t|
  end

  create_table :books, force: true do |t|
    t.string :format_type
    t.integer :format_id
  end

  create_table :dust_jackets, force: true do |t|
    t.string :hardback_id
  end
end

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end

class Book < ApplicationRecord
  belongs_to :format, polymorphic: true
  has_one :dust_jacket, through: :format, source: :dust_jacket, source_type: "Hardback"
end

class Paperback < ApplicationRecord; end
class Hardback < ApplicationRecord
  has_one :dust_jacket
end

class DustJacket < ApplicationRecord; end

class AuthorTest < Minitest::Test
  def test_association
    dust_jacket = DustJacket.new
    hardback = Hardback.create!
    hardback.dust_jacket = dust_jacket

    book = Book.new
    book.format = hardback
    book.save!

    book.reload
    assert_equal dust_jacket, book.dust_jacket
  end
end

test.log

Finished in 0.024135s, 41.4344 runs/s, 0.0000 assertions/s.

  1) Error:
AuthorTest#test_association:
ActiveRecord::HasOneAssociationPolymorphicThroughError: Cannot have a has_one :through association 'Book#dust_jacket' which goes through the polymorphic association 'Book#format'.
    /home/mbyk/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/activerecord-6.0.0/lib/active_record/reflection.rb:917:in `check_validity!'
    /home/mbyk/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/activerecord-6.0.0/lib/active_record/associations/association.rb:43:in `initialize'
    /home/mbyk/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/activerecord-6.0.0/lib/active_record/associations.rb:237:in `new'
    /home/mbyk/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/activerecord-6.0.0/lib/active_record/associations.rb:237:in `association'
    /home/mbyk/.rbenv/versions/2.7.1/lib/ruby/gems/2.7.0/gems/activerecord-6.0.0/lib/active_record/associations/builder/association.rb:100:in `dust_jacket'
    has_one_polymorphic_association2.rb:67:in `test_association'

1 runs, 0 assertions, 0 failures, 1 errors, 0 skips