gistfile1.rb

require 'chronic'

class DateValidator < ActiveModel::EachValidator
  
  def validate_each(record, attribute, value)
    valid = true
    begin
      y = Chronic.parse(value)
      valid = false unless y
    rescue
      valid = false
    end   
    record.errors[attribute] << (options[:message] || "is not a valid date") unless valid  
  end
end