complex includes.rb

class Child
  belongs_to :master, :polymorphic => true
end

class HumanParent
  has_many :organs
end

class RobotOverlord
  has_many :spark_plugs
  has_many :power_supplies
end

# i want each included master to eager-load their hm relationships, but this
# fails since HumanParent doesn't have spark_plugs, etc.
Child.all(:include => {:master, [:organs, :spark_plugs, :power_supplies]})

# as an epilogue, you can accomplish what I wanted to do by hacking activerecord 
# to not raise the exception.  It is super-easy to do (just see the stacktrace when
# you try to do this and remove that line), but I ended up approaching the problem 
# from the other direction and not needing a hacky solution.