Standalone example showing ActiveRecord generating invalid SQL statements when trying to generate a cache key for a collection that involves joining.

ar-bug-repro.rb

# frozen_string_literal: true

begin
  require "bundler/inline"
rescue LoadError => e
  $stderr.puts "Bundler version 1.10 or later is required. Please update your Bundler"
  raise e
end

gemfile(true) do
  source "https://rubygems.org"
  gem "rails", github: "rails/rails"
  gem "arel", github: "rails/arel"
  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|
    t.timestamps
  end

  create_table :tags, force: true do |t|
    t.timestamps
  end

  create_table :taggables, force: true do |t|
    t.integer :tag_id
    t.integer :item_id
    t.string  :item_type
    t.timestamps
  end
end

class Taggable < ActiveRecord::Base
  belongs_to :tag
  belongs_to :item, :polymorphic => true
end

class Post < ActiveRecord::Base
  has_many :taggables, :as => :item
  has_many :tags, :through => :taggables
end

class Tag < ActiveRecord::Base
  has_many :taggables
end

class BugTest < Minitest::Test
  def test_association_stuff
    tag = Tag.create!

    post = Post.create!
    post.tags = [tag]
    post.save


    q = Post.includes(:taggables => :tag).where(:tags => {:id => tag.id})

    ## NOTE: Uncommenting this line causes the test to pass
    #q.load

    key = q.cache_key

    assert_match /posts\/query-/, key
  end
end