Ransack throws an error when doing a query that joins twice to the same table.

[sebaas]

require 'bundler/inline'

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

  gem 'rails', '6.0.3.4'
  gem 'pg'
  gem 'pry'
  gem 'ransack', '2.4.0', require: false
end

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

ActiveRecord::Base.establish_connection(adapter: 'postgresql', database: 'ransack_test')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :arms, force: true do |t|
    t.string :name
    t.integer :amount_of_finger
  end

  create_table :robots, force: true do |t|
    t.string :name
    t.references :left_arm, index: true, foreign_key: { to_table: :arms }
    t.references :right_arm, index: true, foreign_key: { to_table: :arms }
  end
end

class Robot < ActiveRecord::Base
  belongs_to :right_arm, dependent: :destroy, class_name: 'Arm'
  belongs_to :left_arm, dependent: :destroy, class_name: 'Arm'
end

class Arm < ActiveRecord::Base
  has_one :robot
end

class RansackFindsTheObject < ActiveSupport::TestCase
  def setup
    @left_arm = Arm.create!(name: 'left', amount_of_finger: 6)
    @right_arm = Arm.create!(name: 'right', amount_of_finger: 3)
    @robot = Robot.create!(name: 'Wall-e', left_arm: @left_arm, right_arm: @right_arm)
    @q = {'right_arm_name_eq' => 'right', 'left_arm_name_eq' => 'left'}
  end


  def test_ransack_filtering_works
    assert_includes Robot.ransack(@q).result, @robot
  end
end

This proves the error with Rails version 6.0.3 and Ransack version 2.4.0
This throws an error:

Error:
RansackFindsTheObject#test_ransack_filtering_works:
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "left_arms_robots"
LINE 1: ..."right_arm_id" WHERE ("arms"."name" = 'right' AND "left_arms...

It was also evaluated for an older version of rails (5.2.4) with Ransack version 2.4.0
And this works:

require 'bundler/inline'

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

  gem 'rails', '5.2.4'
  gem 'pg'
  gem 'pry'
  gem 'ransack', '2.4.0', require: false
end

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

ActiveRecord::Base.establish_connection(adapter: 'postgresql', database: 'ransack_test')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :arms, force: true do |t|
    t.string :name
    t.integer :amount_of_finger
  end

  create_table :robots, force: true do |t|
    t.string :name
    t.references :left_arm, index: true, foreign_key: { to_table: :arms }
    t.references :right_arm, index: true, foreign_key: { to_table: :arms }
  end
end

class Robot < ActiveRecord::Base
  belongs_to :right_arm, dependent: :destroy, class_name: 'Arm'
  belongs_to :left_arm, dependent: :destroy, class_name: 'Arm'
end

class Arm < ActiveRecord::Base
  has_one :robot
end

class RansackFindsTheObject < ActiveSupport::TestCase
  def setup
    @left_arm = Arm.create!(name: 'left', amount_of_finger: 6)
    @right_arm = Arm.create!(name: 'right', amount_of_finger: 3)
    @robot = Robot.create!(name: 'Wall-e', left_arm: @left_arm, right_arm: @right_arm)
    @q = {'right_arm_name_eq' => 'right', 'left_arm_name_eq' => 'left'}
  end


  def test_ransack_filtering_works
    assert_includes Robot.ransack(@q).result, @robot
  end
end

Also works for rails 6.1.0.rc2 with Ransack 2.4.0

But for Rails version 6.0.3 and Ransack version 2.3.2 It continues failing

This is related to issue #1151 and #1144

[prsanjay]

I have faced the same issue with Rails 6.0.2 and Ransack 2.4.0

After upgrading Rails version to 6.1.0 it all works well!

[yahonda]

According to git bisect, this issue has been addressed at Rails 6-0-stable branch via rails/rails@f9ba524 .

If Rails 6.0.4 is released this fix should be included.

[kaspernj]

An updated test works for me with Postgres:

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    # Rails master
    gem 'rails', github: 'rails/rails', branch: '6-1-stable'
    # Rails last release
    # gem 'rails'
    gem 'sqlite3'
    gem 'ransack', github: 'activerecord-hackery/ransack'
  GEMFILE

  system 'bundle install'
end

require 'bundler'
Bundler.setup(:default)

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

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(
  adapter: 'postgresql',
  database: 'ransack_test',
  host: 'postgres',
  user: 'username',
  password: 'password'
)
ActiveRecord::Base.logger = Logger.new(STDOUT)

# Display versions.
message = "Running test case with Ruby #{RUBY_VERSION}, Active Record #{
  ::ActiveRecord::VERSION::STRING}, Arel #{Arel::VERSION} and #{
  ::ActiveRecord::Base.connection.adapter_name}"
line = '=' * message.length
puts line, message, line

ActiveRecord::Schema.define do
  create_table :arms, force: true do |t|
    t.string :name
    t.integer :amount_of_finger
  end

  create_table :robots, force: true do |t|
    t.string :name
    t.references :left_arm, index: true #, foreign_key: { to_table: :arms }
    t.references :right_arm, index: true #, foreign_key: { to_table: :arms }
  end
end

class Robot < ActiveRecord::Base
  belongs_to :right_arm, dependent: :destroy, class_name: 'Arm'
  belongs_to :left_arm, dependent: :destroy, class_name: 'Arm'
end

class Arm < ActiveRecord::Base
  has_one :robot
end

class RansackFindsTheObject < ActiveSupport::TestCase
  def setup
    @left_arm = Arm.create!(name: 'left', amount_of_finger: 6)
    @right_arm = Arm.create!(name: 'right', amount_of_finger: 3)
    @robot = Robot.create!(name: 'Wall-e', left_arm: @left_arm, right_arm: @right_arm)
    @q = {'right_arm_name_eq' => 'right', 'left_arm_name_eq' => 'left'}
  end

  def test_ransack_filtering_works
    assert_includes Robot.ransack(@q).result, @robot
  end
end

[deivid-rodriguez]

I'll close since this was addressed in Rails.