Rails 3 model with belongs_to different tables exclusively in each record

I have some models like these:

class Alpha < ActiveRecord::Base
 has_many :items 
end    

class Beta < ActiveRecord::Base
 has_many :items
end

class Item < ActiveRecord::Base
 belongs_to :alpha
 belongs_to :beta
end

But i want Item model in each database record to belong either to an :alpha or to a :beta but NOT both. Any nice way to do it in Rails 3? or should I model it with AlphaIt开发者_JAVA技巧ems and BetaItems instead?

You probably want to use a Polymorphic Association for this. More details - http://guides.rubyonrails.org/association_basics.html#polymorphic-associations

class Alpha < ActiveRecord::Base
  has_many :items, :as => :itemable
end    

class Beta < ActiveRecord::Base
  has_many :items, :as => :itemable
end

class Item < ActiveRecord::Base
  belongs_to :itemable, :polymorphic => true
end