Mixin to add support for expiring keys within Ohm

ohm-expiring.rb

module Ohm
  module Expiring

    def self.included(base)
      base.instance_exec {
        include InstanceMethods
        extend  ClassMethods
      }
    end

    module InstanceMethods
      attr_accessor :expiration

      def initialize(*args)
        super(*args)

        self.expiration ||= self.class.expiration
      end

      def create(*args)
        super(*args)
        set_expiration if valid? and expires?
      end

      def set_expiration
        Ohm.redis.expire(key,               expiration)
        Ohm.redis.expire("#{key}:_indices", expiration)
      end

      def expires?
        Integer === expiration
      end
    end

    module ClassMethods
      def expiration
        @expires ||= nil
      end

      def expires(ttl)
        @expires = ttl.to_i
      end
      alias :expire :expires
    end

  end
end

ohm-expiring_spec.rb

require 'spec_helper'

describe Ohm::Expiring do
  class ExpiringModel < Ohm::Model
    include Ohm::Expiring

    attribute :value
    expires 1.minute
  end

  describe '#initialize' do
    it "should set the expiration" do
      em = ExpiringModel.new
      em.expiration.should == 1.minute.to_i
    end
  end

  context 'When being persisted' do
    it "should have an expiration > 0" do
      em = ExpiringModel.create(:value => "Foo")
      Ohm.redis.ttl(em.key).should be > 0
    end

    it "should have an expiration <= 1 minute" do
      em = ExpiringModel.create(:value => "Foo")
      Ohm.redis.ttl(em.key).should be <= 1.minute.to_i
    end
  end
end