# 查询字段是否为验证字段，如果是验证字段返回 true
  def presence?(poi, field)
    presence_fields = poi.constantize.validators.map do |v|
      v.attributes if v.is_a? ActiveRecord::Validations::PresenceValidator
    end
    # 去 nil 并 二维转一维
    if presence_fields.compact.flatten.include?(field)
      return true
    else
      return false
    end
  end
  end