Hi @Luscha, thanks for the suggestion.
The problem with using the field of the first inherited interface would be that the other interfaces won’t find that field in the type. That won’t be the expected behavior from a user’s perspective. Whether I query f1 using I1 or I2, I should always get it on objects of type T. If I use I1.f1 for storage, I won’t get f1 when I query it using I2.
On the other hand, if we were to use T.f1 as the predicate name for the inherited field, then we will no longer have the Diamond inheritance problem. But, that would introduce a lot of complexity in the GraphQL layer.
So, I would instead suggest not to have a design that can cause such problems, if possible.