Rails - Jan 2007 - ActiveResource cache using memcache-client

I''ve created this class that overrides methods for
find,delete,destroy,reload, and save in activeresource. The code
populates a local memcache daemon and uses that cache for future find
requests. I''m posting it here to get whatever feedback people have.
I''m most interested in the pro/con of inheritance over a mixin and how
such a module might be tested.



$ cat lib/cached_resource.rb
# CachedResource uses memcache to cache HTTP responses from a
# RESTful web application.
#
class CachedResource < ActiveResource::Base
  begin
    @@cache = MemCache.new(''localhost'')
    # test the connection to the Memcache server
    @@cache.get(1)
  rescue MemCache::MemCacheError
    @@cache = nil
  end

  # See ActiveResource::Base.find for method description
  def self.find(*args)
    if args.length == 1 && args.first.is_a?(Fixnum)
      cached_record = self.cache_read(args.first)
      return cached_record if cached_record
    end
    # if find(int) is not a cache hit or if the
    # find is more complex, do the find as normal
    # and cache the answers
    records = super(*args)
    case records
      when Array
        records.each {|r| r.cache_write}
      else
        records.cache_write
    end
    return records
  end

  # See ActiveResource::Base.delete for method description
  def self.delete(*args)
    if args.length == 1 && args.first.is_a?(Fixnum)
      self.cache_delete
    end
    super(*args)
  end

  # See ActiveResource::Base.destroy for method description
  def destroy
    self.cache_delete
    super
  end

  # See ActiveResource::Base.reload for method description
  def reload
    self.cache_delete
    # This is lifted from ActiveResource::Base.reload and modified
    # to pass along the grant argument.
    self.load self.class.find(id, @prefix_options).attributes
  end

  # See ActiveResource::Base.reload for method description
  def save
    super
    self.cache_write
  end

  def self.build_cache_key(id)
    "#{name}:#{id}"
  end

  def self.cache_read(id)
    @@cache.get(self.build_cache_key(id)) if @@cache
  end

  def self.cache_delete(id)
    @@cache.delete(self.build_cache_key(id)) if @@cache
  end

  def cache_key
    self.class.build_cache_key(self.id)
  end

  def cache_write
    @@cache.set(self.cache_key,self) if @@cache
  end

  def cache_delete
    @@cache.delete(self.cache_key) if @@cache
  end

end



Thanks,
Don
ps. The code above is released under the same license as the ruby language.

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