Merge STI associations with "or" ArgumentError (Relation passed to #or must be structurally compatible. Incompatible values: [:create_with])

[humphreyja]

I am trying to merge 2 has_many STI associations for the same table. It looks like the only way this will work is if I set create_with(nil) for both associations before merging with or.

Steps to reproduce

# frozen_string_literal: true

begin
  require 'bundler/inline'
rescue LoadError => e
  warn 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

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

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

  gem 'rails', '6.0.3.2'
  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 :invoices, force: true do |t|
    t.string :name
  end

  create_table :receivables, force: true do |t|
    t.string :type
    t.integer :invoice_id
  end
end

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

class Receivable < ApplicationRecord
   belongs_to :invoice
end

class Payment < Receivable
end

class AppliedCredit < Receivable
end

class Invoice < ApplicationRecord
  has_many :payments, class_name: ::Payment.to_s, foreign_key: :invoice_id
  has_many :applied_credits, class_name: ::AppliedCredit.to_s, foreign_key: :invoice_id

  def all_payments
    payments.or(applied_credits)
  end
end

class BugTest < Minitest::Test
  def test_association_stuff
    invoice = Invoice.create!

    payment = Payment.create!(invoice: invoice)
    applied_credit = AppliedCredit.create!(invoice: invoice)
    
    assert_equal invoice.all_payments.pluck(:id), [payment.id, applied_credit.id]
  end
end

Expected behavior

invoice.all_payments should return all receivables of type Payment and AppliedCredit

Actual behavior

ArgumentError (Relation passed to #or must be structurally compatible. Incompatible values: [:create_with])

System configuration

Rails version: 6.0.3.2

Ruby version: 2.6.6

[KapilSachdev]

Error is expected because finder conditions will be set for create_with and where once STI is sensed.
Your test case will pass if ignore_default_scope is set to true (not recommended)

class Receivable < ApplicationRecord
  belongs_to :invoice
  self.ignore_default_scope = true
end

rails/activerecord/lib/active_record/core.rb

Lines 318 to 327 in 1d6daaa

	def relation
	relation = Relation.create(self)
	if finder_needs_type_condition? && !ignore_default_scope?
	relation.where!(type_condition)
	relation.create_with!(inheritance_column.to_s => sti_name)
	else
	relation
	end
	end