Validator for an array with a whitelist.

recruit.rb

# app/models/forms/recruit.rb
class Forms::Recruit
  include ActiveModel::Model
  attr_accessor :job_types
  validates :job_types, presence: true, white_list: {list: JOB_TYPES, allow_blank: true}
end

white_list_validator.rb

# app/validators/whitelist_validator.rb
# frozen_string_literal: true

class WhitelistValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    return if options[:allow_empty] && value.blank?
    return record.errors.add(attribute, :inclusion) if value.blank?
    record.errors.add(attribute, :inclusion) if value.any?{|v| options[:list].exclude?(v)}
  end
end