[RUBY] Implementation policy to dynamically save and display Timezone in Rails

Background and requirements

There was a request to save the time of an event such as Meeting considering all time zones.

For example Meeting1 will be held in Tokyo from 11:00. Meeting2 will be held in UTC from 10:00.

I want to express something like.

Implementation procedure

--Fix the default Timezone of Rails API server. --Save Timezone in DB --Determine where to insert the logic that dynamically changes the Timezone. --Check if time type is saved in DB considering timezone --Validation to prevent passing strings without timezone information when saving

Pin the default Timezone of the Rails API server.

First, Rails has multiple time zones to consider.


This time, to avoid confusion, I set all Timezones below to UTC.

Save Timezone in DB

Save the variable that is the basis for changing the timezone. Since the timezone is changed via ActiveSupport, you can write the following validation so that the valid value is saved.

# tz :string
class Meeting < ApplicationRecord 

validates :tz, inclusion: { in: ActiveSupport::TimeZone::MAPPING.values }, presence: true


Decide where to insert the logic to change the timezone to dynamic at the time of GET with API.

When returning a value in the API, add logic that dynamically changes the Timezone and returns the time. In this case, I incorporated it into Serialzer. Since this logic is related to display, as a result, we decided to put it in a layer close to View.

#  tz :string
class Meeting < ApplicationRecord 

  def timezone

  def use_timezone
    Time.use_zone(timezone) do

class MeetingSerializer

  attribute :start_time do |record|
    record.use_timezone do


Check if the time type is saved in the DB considering the timezone

Save is with timezone information, if you pass a string, ActiveRecord will do it nicely.

# actieve_The timezone of record is UTC

[47] pry(main)> meeting
=> #<Meeting:0x00007ff2c7ad4618
 id: "162b1ed7-5502-42f8-8bed-592d2dae7db1",
 start_at: Mon, 05 Oct 2020 16:00:00 UTC +00:00,
 created_at: Tue, 06 Oct 2020 06:28:39 UTC +00:00,
 updated_at: Thu, 08 Oct 2020 02:11:54 UTC +00:00>
[48] pry(main)> meeting.start_at="2020-10-06T01:00:00+0900"
=> "2020-10-06T01:00:00+0900"
[49] pry(main)> meeting.start_at
=> Mon, 05 Oct 2020 16:00:00 UTC +00:00

Validation so that strings without timezone information are not passed when saving

I created a controller module like the one below, and made validation bite with before_action.

module ValidateTimeFormat
  class TimeFormatError < StandardError

  extend ActiveSupport::Concern

  included do
    rescue_from ValidateTimeFormat::TimeFormatError, with: :render_time_format_error


  def render_time_format_error(msg)
    render json: { message: msg }, status: :bad_request

  def validate_time_format(time_str)
    DateTime.strptime(time_str, TIME_FORMAT).zone
  rescue Date::Error
    raise ValidateTimeFormat::TimeFormatError, :time_format_is_invalid


Rails had an image that there are many points to consider in the Time system. With this implementation, I fully understood ()

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