How to validate the date such that it is after today in Rails?

Question

I have an Active Record model that contains attributes: expiry_date. How do I go about validating it such that it is after today(present date at that time)? I am totally new to

Answer 1

In rails 4+ there are future? and past? methods for DateTime objects, so a simpler answer is

class Invoice < ActiveRecord::Base
  validate :expiration_date_cannot_be_in_the_past

  def expiration_date_cannot_be_in_the_past
    if expiration_date.present? && expiration_date.past?
      errors.add(:expiration_date, "can't be in the past")
    end
  end    
end