app/models/worker.rb
class Worker < ActiveRecord::Base
belongs_to :case_file
validates :case_file, presence: true
validate :nationality_cannot_be_others
enum english_proficiency: [:poor, :basic, :intermediate, :advanced]
private
def nationality_cannot_be_others
errors.add(:nationality, "Please specify nationality") if nationality == 'Others' || nationality.blank?
end
end