ambiguity

I wanted a Django model with 2 foreign keys from the same table. It's an event table which has 2 columns for employees: the 'actor' and the 'receiver'. But I get this error: Error: One or more models did not validate: tasks.task: Intermediary model TaskEvent has more than one foreign key to Employee, which is ambiguous and is not permitted. Is there a better way to model this? Thanks I think I'm going to add a TaskEvent_to_Employee table. There will be two records in it, one for each of the two employees related to each TaskEvent . Anyone know an easier workaround? I haven't done this yet, but

Suppose I have this variadic base class-template: template <typename ... Types> class Base { public: // The member foo() can only be called when its template // parameter is contained within the Types ... pack. template <typename T> typename std::enable_if<Contains<T, Types ...>::value>::type foo() { std::cout << "Base::foo()\n"; } }; The foo() member can only be called when its template-parameter matches at least one of the parameters of Base (the implementation of Contains is listed at the bottom at this post): Base<int, char>().foo<int>(); // fine Base<int, char>().foo<void>(); // error Now