ActiveRecord::Timestamp

active record 在create/update的时候会默认更新created_at/updated_at字段为当前字段，可以通过config.active_record.record_timestamps设置关闭。
可以通过config.active_record.default_timezone设置时区，等等功能不一一罗列。

# frozen_string_literal: true

module ActiveRecord
  module Timestamp
    extend ActiveSupport::Concern

    included do
      class_attribute :record_timestamps, default: true
    end

    def initialize_dup(other) # :nodoc:
      super
      clear_timestamp_attributes
    end

    module ClassMethods # :nodoc:
      def touch_attributes_with_time(*names, time: nil)
        attribute_names = timestamp_attributes_for_update_in_model
        attribute_names |= names.map(&:to_s)
        attribute_names.index_with(time || current_time_from_proper_timezone)
      end

      def timestamp_attributes_for_create_in_model
        @timestamp_attributes_for_create_in_model ||=
          (timestamp_attributes_for_create & column_names).freeze
      end

      def timestamp_attributes_for_update_in_model
        @timestamp_attributes_for_update_in_model ||=
          (timestamp_attributes_for_update & column_names).freeze
      end

      def all_timestamp_attributes_in_model
        @all_timestamp_attributes_in_model ||=
          (timestamp_attributes_for_create_in_model + timestamp_attributes_for_update_in_model).freeze
      end

      def current_time_from_proper_timezone
        default_timezone == :utc ? Time.now.utc : Time.now
      end

      private
        def timestamp_attributes_for_create
          ["created_at", "created_on"]
        end

        def timestamp_attributes_for_update
          ["updated_at", "updated_on"]
        end

        def reload_schema_from_cache
          @timestamp_attributes_for_create_in_model = nil
          @timestamp_attributes_for_update_in_model = nil
          @all_timestamp_attributes_in_model = nil
          super
        end
    end

  private

    def _create_record
      if record_timestamps
        current_time = current_time_from_proper_timezone

        all_timestamp_attributes_in_model.each do |column|
          if !attribute_present?(column)
            _write_attribute(column, current_time)
          end
        end
      end

      super
    end

    def _update_record
      if @_touch_record && should_record_timestamps?
        current_time = current_time_from_proper_timezone

        timestamp_attributes_for_update_in_model.each do |column|
          next if will_save_change_to_attribute?(column)
          _write_attribute(column, current_time)
        end
      end

      super
    end

    def create_or_update(touch: true, **)
      @_touch_record = touch
      super
    end

    def should_record_timestamps?
      record_timestamps && (!partial_writes? || has_changes_to_save?)
    end

    def timestamp_attributes_for_create_in_model
      self.class.timestamp_attributes_for_create_in_model
    end

    def timestamp_attributes_for_update_in_model
      self.class.timestamp_attributes_for_update_in_model
    end

    def all_timestamp_attributes_in_model
      self.class.all_timestamp_attributes_in_model
    end

    def current_time_from_proper_timezone
      self.class.current_time_from_proper_timezone
    end

    def max_updated_column_timestamp
      timestamp_attributes_for_update_in_model
        .map { |attr| self[attr]&.to_time }
        .compact
        .max
    end

    # Clear attributes and changed_attributes
    def clear_timestamp_attributes
      all_timestamp_attributes_in_model.each do |attribute_name|
        self[attribute_name] = nil
        clear_attribute_changes([attribute_name])
      end
    end
  end
end