Rails timestamptz migration

description.txt

docker-compose --run --rm ruby test.rb

docker-compose.yml

version: '3'
services:
  ruby:
    image: ruby:2.3
    depends_on:
      - db
    working_dir: /opt/project
    environment:
      - TZ=Europe/Moscow
    volumes:
    - .:/opt/project
    - ./volumes/ruby/bundle:/usr/local/bundle
    command: ruby test.rb

  db:
    image: postgres:9.3

test.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', '~> 5.0', '>= 5.0.6'
  gem 'pg'
  gem 'rspec'
  gem 'pry-byebug'
end

require 'logger'
require 'pry-byebug'
require 'rails/all'
require 'active_record'
require 'rspec'
require 'rspec/autorun'

DATABASE_TIMEZONE = 'UTC' # Works without migrations this way
# DATABASE_TIMEZONE = 'Europe/Moscow'

ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Base.establish_connection(
  adapter: 'postgresql',
  user: 'postgres',
  database: 'postgres',
  host: 'db',
  pool: 1
)

binding.pry

# Do it before the fixing migration
ActiveRecord::Base.connection.execute("SET TIME ZONE '#{DATABASE_TIMEZONE}'")

ActiveRecord::Schema.define do
  create_table :assignments, force: true do |t|
    t.column :assigned_at, 'timestamp with time zone'
  end
end

class Assignment < ActiveRecord::Base
end

OLD_ASSIGNMENT_CURRENT_TIME = Time.parse('2000-06-11 10:05:05 +0300').utc
NEW_ASSIGNMENT_CURRENT_TIME = Time.parse('2019-03-11 10:05:05 +0300').utc

TEST_OLD_ASSIGNMENT_ID = 100001
TEST_NEW_ASSIGNMENT_ID = 100000

# Assigment created with time in daylight saving
Assignment.create(id: TEST_OLD_ASSIGNMENT_ID, assigned_at: OLD_ASSIGNMENT_CURRENT_TIME)

# Assignment created with time without daylight saving
Assignment.create(id: TEST_NEW_ASSIGNMENT_ID, assigned_at: NEW_ASSIGNMENT_CURRENT_TIME)

class MigrateAssignmentTimestamptz < ActiveRecord::Migration[5.2]
  def up
    change_column :assignments, :assigned_at, :timestamp
  end
end

MigrateAssignmentTimestamptz.migrate(:up)

RSpec.describe Assignment do
  let(:current_time) { Time.parse('2019-03-11 10:05:05 +0300').utc }

  around do |example|
    # Database reset
    Assignment.transaction do
      example.call
      raise ActiveRecord::Rollback
    end
  end

  before do
    db_timezone = ActiveRecord::Base.connection.execute('SHOW TIMEZONE').first.dig('TimeZone')
    expect(db_timezone).to eq(DATABASE_TIMEZONE)
  end

  specify 'migration should fix existing old rows to have correct time' do
    assignment = Assignment.find(TEST_OLD_ASSIGNMENT_ID)
    expect(assignment.reload.assigned_at).to eq(OLD_ASSIGNMENT_CURRENT_TIME)
  end

  specify 'migration should fix existing fresh rows to have correct time' do
    assignment = Assignment.find(TEST_NEW_ASSIGNMENT_ID)
    expect(assignment.reload.assigned_at).to eq(NEW_ASSIGNMENT_CURRENT_TIME)
  end

  it 'keeps timezone between saving and reading' do
    assignment = Assignment.create(assigned_at: current_time)
    expect(assignment.reload.assigned_at).to eq(current_time)
  end
end