btrc-hub/backend/app/models/post_version.rb

class PostVersion < ApplicationRecord
  before_update do
    raise ActiveRecord::ReadOnlyRecord, '版は更新できません．'
  end

  before_destroy do
    raise ActiveRecord::ReadOnlyRecord, '版は削除できません．'
  end

  belongs_to :post
  belongs_to :parent, class_name: 'Post', optional: true
  belongs_to :created_by_user, class_name: 'User', optional: true

  enum :event_type, { create: 'create',
                      update: 'update',
                      discard: 'discard',
                      restore: 'restore' }, prefix: true, validate: true

  validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
  validates :event_type, presence: true, inclusion: { in: event_types.keys }
  validates :url, presence: true

  validate :validate_original_created_range

  scope :chronological, -> { order(:version_no, :id) }

  private

  def validate_original_created_range
    f = original_created_from
    b = original_created_before
    return if f.blank? || b.blank?

    if f >= b
      errors.add :original_created_before, 'オリジナルの作成日時の順番がをかしぃです．'
    end
  end
end