Sorry for bad English. Why we have so restriction in ActiveRecord?
/usr/lib/ruby/gems/1.8/gems/activerecord-2.3.9/test/cases/ nested_attributes_test.rb
def test_should_raise_argument_error_if_trying_to_build_polymorphic_belongs_to assert_raise_with_message ArgumentError, "Cannot build association looter. Are you trying to build a polymorphic one-to-one association?" do Treasure.new(:name => 'pearl', :looter_attributes => {:catchphrase => "Arrr"}) end end
