I’m upgrading blippr to Rails 2.3. Here are some of the things that had to be changed to upgrade:

Switch the application entirely to LibXML for all its XML parsing needs

In config/environment.rb: Add the following

ActiveSupport::XmlMini.backend = 'LibXML'

This means that the faster_xml_simple monkeypatch is no longer needed. I don’t think we’re doing much else with XML on blippr, but it’ll be nice to have libxml-backed parsing all around. I must not use REXML. REXML is the app-killer. REXML is the little-death that brings total obliteration.

Fixes for will_paginate and SQL errors when counting records with a custom :select clause

Upgrade will_paginate. Even after the upgrade, something about 2.3’s named scope handling was still breaking my app. I have a named scope like so:

  :select => "*, (blips.vote_score+2)/WEIGHT_FACTOR as weighted_score",
  :order => "weighted_score desc"

This was causing .paginate calls with this named scope to fail with an invalid SQL error. will_paginate should automatically clobber :select phrases before attempting to count records, but it wasn’t. The solution is to specify a :count condition to my .paginate calls with the right select clause.

Blip.best.paginate(:page => current_page, :per_page => 30, :count => {:select => "blips.id"})

In general, any paginate call with a :select specified seems to break. The :count clause fixes them.

Upgrade my libmemcached plugin

A lot of the internal session stuff has changed. We use Evan Weaver’s libmemcached client, and an upgraded copy of 37signals’ libmemcached store for Rails. The plugin’s been upgraded to work with 2.3, and provides a session store on top of the general Rails store.

Our caching config now looks something like this:

GENERAL_CACHE_SERVERS = ["localhost:11211"]
GENERAL_CACHE_OPTIONS = {:untaint => true}
SESSION_CACHE_SERVERS = ["localhost:11212"]
SESSION_CACHE_OPTIONS = { :prefix_key => "session:blippr" }
SESSION_MEMCACHE_CLIENT = Memcached.new(SESSION_CACHE_SERVERS, SESSION_CACHE_OPTIONS)

config.cache_store = :libmemcached_store, GENERAL_CACHE_SERVERS, GENERAL_CACHE_OPTIONS
config.action_controller.session_store = :libmemcached_store
config.action_controller.session = {
  :cache => SESSION_MEMCACHE_CLIENT,
  :expires_after => 86400
}

Works great with libmemcached, with separate memcached instances for fragments and sessions (so that an over-populated fragment store won’t start clobbering sessions).

Update query parsing

I parse query parameters for some funky filtering. In 2.2.2 I used:

ActionController::AbstractRequest.parse_query_parameters(query_string)

In 2.3, that becomes:

Rack::Utils.parse_query(query_string)

That’s about it for now, but as problems arise I’ll be sure to add them.