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.

This is mostly for my own reference, but also because I couldn’t find any great help while googling the problem.

I’m working on switching from memcache-client to Evan Weaver’s libmemcached gem, and it’s gone well, except for one nagging error:

libmemcached.so.2: cannot open shared object file: No such file or directory - /opt/ruby-enterprise-1.8.6-20081215/lib/ruby/gems/1.8/gems/memcached-0.13/lib/rlibmemcached.so

libmemcached.so.2 was absolutely there, in my /usr/local/lib path. However, ldd was showing that rlibmemcached.so wasn’t properly linked to that library. The solution was the following:

[root@polaris libmemcached-0.25.14]# ./configure --prefix=/usr
[root@polaris libmemcached-0.25.14]# make && make install

ldd now shows the proper reference, and everything works. All better!

Back in September, I wrote about making your REST APIs more flexible and easier to maintain. I’ve been working with this code with great success for the past few months, and have improved and tweaked it. It’s changed enough that it’s time for another blog post about it.

First off, the render method signature has changed. This is for full Rails compatiblity, including Rails 2.3. It’ll work as you’d expect without any unpleasant surprises. Secondly, there are some other optional render targets, designed for leveraging existing #to_xml handlers where you already like them.

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