Validation using :if or :unless conditions

gistfile1.rb

class EmploymentInformation < ActiveRecord::Base
  attr_accessible :employment_status_id, :company_name, :university
                  
  validates :employment_status_id, :presence => true, :inclusion => { :in => proc { |req| req.employment_status_types.map{ |key, value| key } } }
  validates :company_name,    :presence => true, :format => { :with => /\A[A-z\s\-\._]+\z/ }, :unless => proc { |req| req.employment_status.nil? }
  validates :university,            :presence => true, :format => { :with => /\A[A-z\s\-\._]+\z/ }, :unless => proc { |req| req.employment_status.nil? }

end