Eager loading of polymorphic associations doesn't work in Rails < 2.1 and only works in 2.1 if rails doesn't have to fall back on left outer joins for the :include.
This plugin allows eager loading in all situations in rails.
It assumes you are using the default "_type" suffix. With this code you can just use a :include directive in your finds and it will return your associations instead of throwing an exception.
To install as a rails plugin, use the script/plugin command with rails >= 2.0
./script/plugin install git://github.com/haruska/polymorphic_include.git
For rails < 2.0, install it by hand
cd vendor/plugins git clone git://github.com/haruska/polymorphic_include.git
class Address < ActiveRecord::Base belongs_to :addressable, :polymorphic => true end # A call that tries to eager load the addressable model Address.find(:all, :include => :addressable)
Copyright (c) 2008-2009 Jason Haruska, released under the MIT license