Scenario from issue with the use of postgres's unnest query in array columns on rails 4.2

rails-4-2-unnest-query-in-array-columns.rb

# Activate the gem you are reporting the issue against.
# gem 'activerecord', '4.1.9' # test passing
gem 'activerecord', '4.2.0' # test failing
require 'active_record'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
con = ActiveRecord::Base.establish_connection(
  :adapter  => "postgresql",
  :host     => "localhost",
  :username => "postgres",
  :password => "123",
  :database => "rails_test"
)
ActiveRecord::Base.logger = Logger.new(STDOUT)
con.connection.execute("DROP TABLE IF EXISTS logs;");

ActiveRecord::Schema.define do
  create_table :logs do |t|
    t.string :name
    t.string :tags, array: true, default: []
    t.index :tags, using: 'gin'
  end
end

class Log < ActiveRecord::Base
  def self.all_tags
    select('unnest(tags) as id').map(&:id).uniq
  end
end

Tags1 = ['bar', 'lol', 'foo']
Tags2 = ['car', 'plane']
Log.create(name: 'test', tags: Tags1)
Log.create(name: 'number 2', tags: Tags2)

puts Log.first.tags
puts Log.last.tags

puts Log.all_tags

class LogTest < Minitest::Test
  def test_unnset
    tags = Tags1 + Tags2

    assert_equal tags, Log.all_tags
  end
end