问如何将实例方法转换为关联？

EN

add_reference :subscriptions, 
              :current_version,
              foreign_key: {
                to_table: :versions  ​
             ​}

class Subscription < ApplicationRecord
  has_many :versions, 
    after_add: :set_current_version
  belongs_to :current_version,
    class_name: 'Version'

  def set_current_version(version)
     update_attribute(:current_version_id, version.id) 
  end
end

class Subscription
  has_one :current_version, 
    -> {
      where(
        id: Version.select(:id)
                   .group(:subscription_id)
                   .order("MAX(versions.authorized_at) ASC")
      )
    },
    class_name: 'Version'
end

  scope :with_current_version, -> {
    select("subscriptions.*, last_version.authorized_at AS last_version_authorized_at")
      .joins("LEFT OUTER JOIN (SELECT DISTINCT ON (subscription_id) * FROM versions
      ORDER BY versions.subscription_id,
      versions.authorized_at DESC) AS last_version
      ON last_version.subscription_id = subscriptions.id")
  }

@subscriptions = current_account.subscriptions.with_current_version
                         .order("last_version_authorized_at ASC")