Support for property resolvers for interface types

I’m submitting a…

[x] Feature request

Current behavior

I would like to create a resolver for an interface type which has a property resolver

Expected behavior

I should be able to define a resolver for an interface type and add property resolvers for virtual fields on that resolver. It should have access to services via constructor injection, etc.

Minimal reproduction of the problem with instructions

@InterfaceType()
export class IExample {
}

@Resolver(of => IExample)
export class ExampleResolver {
  constructor(
    private readonly example: ExampleService
  ) { }

  @ResolveProperty(type => Boolean)
  public async foo(@Root() item: IExample) {
    // this.example is available for this function
    return false
  }
}

What is the motivation / use case for changing the behavior?

If you have an interface type with multiple concrete types you want to be able to access it in gql like:

examples {
  foo
}

Not

examples {
  ... on ConcreteType {
    foo
  }
}

Which it seems like right now the only way to do it is to promote the field to resolvers for each concrete type.

Environment

Nest version: ^6.7.2 For Tooling issues:

• Node version: v12.8.0
• Platform: linux

[justinmchase]

Looking at this more, adding the field to the interface doesn’t help. I am getting a crash in type-graphql which I’m filing a bug over there for but I do think that this is a legitimate issue in this library and think this ticket should be re-opened.

I think its legitimate because I am able to do this with graphql without using this library and it is documented in their documentation and it is a limitation of this library that this isn’t supported.

I think the example from the gql documentation for characters that @marcus-sa linked to is a good one, so this feature request / bug becomes how can I implement Character.name as a property resolver?

@InterfaceType()
export class Character {
  @Field()
   public name: string
}

@Resolver(of => Character ) // <-- this crashes my app
export class CharacterResolver {
  constructor(
    private readonly characters: CharacterService
  ) { }

  @ResolveProperty(type => String)
  public async name(@Root() character: Character) {
    return this.charcters.resolveName(character)
  }
}

[marcus-sa]

You can’t query interfaces, you can only implement them.

EDIT: It seems like I’ve misunderstood your question. This is out of the scope (as it’s not supported in the GraphQL spec)