base_validator.rb

class BaseValidator
  include ActiveModel::Validations

  def initialize(record_params = {})
    self.class.fields.each do |field|
      val = record_params[field]
      send("#{field}=", val)
    end
  end
end

class NameValidator < BaseValidator
  def self.fields
    [:name]
  end

  attr_accessor(*fields)

  validates :name, presence: true
  validates :name, length: { maximum: A9n.validations[:max_text_field_size] }
end