my_date_validation.rb

module ActiveRecord
  module Validations
    module ClassMethods
      def validates_as_date(*attr_names)
        configuration = {
          :message   => 'is invalid date format',
          :allow_nil => true }
#        configuration.update(attr_names.pop) if attr_names.last.is_a?(Hash)
        debugger
        validates_each(attr_names, configuration) do |record, attr_name, value|
          debugger
          date = Date.strptime(value, '%Y-%m-%d') rescue nil
          if date.nil?
            record.errors.add(attr_name, configuration[:message])
          end
        end
      end
    end
  end
end