Enable easy modeling of errors using unions

[kaqqao]

A popular use for unions is to model errors, as this talk exemplifies nicely. SPQR should have an easy way to enable this.

An approach could be to map (chosen) exceptions declared by a resolver method as union members, in addition to the return type.

As always, it must be reasonably easy to extend by the user.

[ssiemens-hm]

Would look forward to this feature too

[kaqqao]

I do plan to pick it up very soon.

[codelizrd]

Maybe it's an idea to auto make a Union type of the result type and all the declared thrown Exceptions? Like this:

@GraphQLQuery
public Customer fetchCustomerById(
   @GraphQLArgument(name = "id") String id
) throws ObjectNotFoundException 
{
   Customer customer = CustomerDB.byId(id);
   if (customer == null) {
      throw new ObjectNotFoundException("Not found");
   }
   return customer;
}

Results in schema

fetchCustomerById(id: String!): FetchCustomerByIdResponse!
union FetchCustomerByIdResponse =
FetchCustomerByIdResponse_Customer
FetchCustomerByIdResponse_ObjectNotFoundException

[TheNaqvi]

Any plans to work on this @kaqqao ? It would be a fantastic addition to the library. I foresee that maybe the absence of this might be the reason for us to stop using this library for our project.

[yashb042]

@kaqqao Any updates on this? As @TheNaqvi mentioned, this is a major thing, and without it, the library is not useful for effective error handling.