Migration example with stubbed models

migration_example.rb

class MergePaypalVerificationAndContacts < ActiveRecord::Migration[7.0]
  class User < ApplicationRecord
    self.table_name = :users
    has_many :user_verifications, class_name: 'UserVerification'
    has_one :paypal_verification, class_name: 'OldPaypalVerification'
  end

  class UserVerification < ApplicationRecord
    self.table_name = :user_verifications
    self.inheritance_column = :_type_disabled
    belongs_to :user, inverse_of: :user_verifications
    belongs_to :contact, inverse_of: :user_verification
    enum _prefix: true, type: { personal: 0, corporate: 1, paypal: 2 }
  end

  class OldPaypalVerification < ApplicationRecord
    self.table_name = :paypal_verifications
    belongs_to :user
    belongs_to :country
  end

  class Contact < ApplicationRecord
    self.table_name = :contacts
    has_one :user_verification, class_name: 'UserVerification'
    belongs_to :country
    belongs_to :entity, polymorphic: true
  end

  class NewPaypalVerification < Contact
    self.table_name = :contacts
    self.inheritance_column = :_type_disabled

    default_scope { where(paypal: true) }
    enum account_type: { personal: 0, corporate: 1 }

    validates :account, :country, :address, :entity, :user, presence: true
    validates :entity_id, uniqueness: { scope: %i[entity_type], conditions: -> { where(paypal: true) } }

    alias_attribute :user, :entity
    alias_attribute :account, :email
    alias_attribute :account_type, :type
    alias_attribute :user_id, :entity_id
  end

  def up
    add_column :contacts, :verified, :boolean, default: :false
    add_column :contacts, :paypal, :boolean, default: :false

    Contact.reset_column_information
    NewPaypalVerification.reset_column_information

    # Итерируем PaypalVerification
    # переносим в Contact данные
    # обновляем Все связанные UserVerification привязывая верификацию к конкретному контакту
    OldPaypalVerification.find_each do |pv|
      params = pv.attributes.merge(entity_type: 'User', paypal: true).except!('id')
      contact = NewPaypalVerification.create!(params)
      uv_paypal = pv.user.user_verifications.type_paypal.first

      uv_paypal.update(contact: contact) if uv_paypal
    end
  end

  def down
    raise 'Not Implemented'
  end
end