如何在引用相同模型两次时使用嵌套曝光？

Question

我有一个Contact模型的葡萄实体，它引用了User模型两次：

SELECT id,
       group_id,
       object_id,
       object,
       param,
       (SELECT count(*)
        FROM controlled_object AS co2
        WHERE group_id = controlled_object.group_id)
FROM controlled_object;

当我得到一个提供联系的端点时，我有以下错误

class Contact < ApplicationRecord
  belongs_to :user, foreign_key: :user_id
  belongs_to :contact, class_name: 'User', foreign_key: :contact_id

  def entity
    Entity.new(self)
  end

  class Entity < Grape::Entity
    expose :contact do
      expose :id
      expose :user, as: :inviter, merge: true, using: User::Entity
      expose :contact, as: :invitee, merge: true, using: User::Entity
      expose :status
    end
  end
end

如何使其包含联系人实体中的邀请者和被邀请者的用户实体？