Polymorphic select

models.rb

class Catch < ActiveRecord::Base
  belongs_to :animal, :polymorphic => true
end

class Bird < ActiveRecord::Base
  attr_accessible :name
  has_one :catch, :as => :animal
end

class Fish < ActiveRecord::Base
  attr_accessible :name
  has_one :catch, :as => :animal, :dependent => :destroy
end

output.html

<select>
  <optgroup label="Fish"><!-- That's a polymorphic class -->
    <option value="Fish_1">Trout</option>
    <option value="Fish_2">Salmon</option>
  </optgroup>
  <optgroup label="Bird"><!-- That's another polymorphic class -->
    <option value="Bird_1">Eagle</option>
    <option value="Bird_2">Pigeon</option>
  </optgroup>
</select>