gistfile1.txt

class Video < ActiveRecord::Base
  inherits_from :item
end

class Article < ActiveRecord::Base
  inherits_from :item
end

class Item < ActiveRecord::Base
  has_many :responses
end

class Response < ActiveRecord::Base
  belongs_to :item
  validates_presence_of :item_id
end

# in console:
# 

# saving a new video item (maybe at items/video/new) 
v  = Video.new
v.save # true

# saving a response to that (video) item 
r = Response.new
r.item = Item.find(1) #causes error

# error:
# 
# ActiveRecord::AssociationTypeMismatch: Item(#2157741480) expected, got Video(#2155124540)