rails_mysql_limit_having_issue.rb

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', '4.2.7'
    # gem 'sqlite3'
    gem "mysql2"
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

# This issue does not appear to happen on sqlite3, but I'm unsure whether this is the (mysql) Rails adapter failing, or the actual driver failing
# Toggle this and the mysql gem and driver to see for yourself
# ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')

# Change username/password accordingly and create database manually
ActiveRecord::Base.establish_connection(adapter: 'mysql2', host: 'localhost', username: 'root', password: '', database: 'gist_test')

ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :baskets, force: true do |t|
    t.integer :required_amount_of_apples
  end

  create_table :apples, force: true do |t|
    t.integer :basket_id
    t.integer :amount_of_stems
  end
end

class Basket < ActiveRecord::Base
  has_many :apples
end

class Apple < ActiveRecord::Base
  belongs_to :basket
end

class BugTest < ActiveSupport::TestCase
  # This test fails with:
  # ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'baskets.required_amount_of_apples' in 'having clause'
  def test_failing_magic
    assert_nothing_raised do
      Basket.includes(:apples)
        .group(:id)
        .having("baskets.required_amount_of_apples != COUNT(DISTINCT apples.amount_of_stems)")
        .limit(1)
        .pluck("baskets.required_amount_of_apples, baskets.id")
    end
  end

  # This test passes.
  def test_passing_magic
    assert_nothing_raised do
      Basket.includes(:apples)
        .group(:id)
        .having("baskets.required_amount_of_apples != COUNT(DISTINCT apples.amount_of_stems)")
        .pluck("baskets.required_amount_of_apples, baskets.id")
      end
  end
end