domain.rb

class DomainValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless domain_check(value)
      record.errors[attribute] << (options[:message] || "is not a valid domain")
    end
  end
   def domain_check(name)
    input = PublicSuffix.parse(name)
    domain = input.domain
    PublicSuffix.valid?(domain)
  end
end
 

class Domain < ActiveRecord::Base
  validates :name, uniqueness: true, domain: true, presence: true, length: { maximum: 50 }
 end