Cached sequence

cached_sequence.rb

class CachedSequence
  extend ActiveSupport::Memoizable

  def initialize(cache_key)
    @cache_key = cache_key
    ensure_value
  end

  def next
    Rails.cache.increment(cache_key)
  end

  def delete
    Rails.cache.delete(cache_key)
  end

  def reset
    delete
    ensure_value
  end

private

  def ensure_value
    Rails.cache.fetch(cache_key) { 0 }
  end

  def cache_key
    "CACHED_SEQUENCE:#{@cache_key}"
  end
  memoize :cache_key

end

cached_sequence_spec.rb

require 'spec_helper'

describe "a sequence backed by a cache" do
  subject { CachedSequence.new('test-seq') }
  before(:each) { subject.reset }
  it "should have 1 for its initial value" do
    subject.next.should == 1
  end
  it "should increment by 1 for each requested value" do
    subject.next
    subject.next.should == 2
  end
  it "should be possible to delete a sequence" do
    subject.next
    subject.delete
    subject.next.should == nil
  end
  it "should be possible to reset a sequence" do
    subject.next
    subject.reset
    subject.next.should == 1
  end
  context "cache-like features" do
    let!(:other_with_same_cache_key) { CachedSequence.new('test-seq') }
    it "should be able to find the same cached information via a different instance" do
      seq = subject.next
      seq.should == other_with_same_cache_key.next - 1
    end
  end
end