ar_test.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", "6.0.4"
  gem "activerecord", "6.1.4"
  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 :posts, force: true do |t|
  end

  create_table :comments, force: true do |t|
    t.integer :x_post_id
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post, foreign_key: :x_post_id
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!
    Comment.create!(x_post_id: post.id)

    comments = Comment.eager_load(:post).select(:id)
    assert_equal post.id, comments.first.x_post_id
    # 6.1.4
    #=> ActiveModel::MissingAttributeError: missing attribute: x_post_id
  end
end