Typescript: how to handle resolvers that return partial data?

[aryzing]

With Apollo, resolvers are allowed to return partial data, which is then fed into the object type resolver to fill in the rest. For example:

const resolvers = {
  Query: {
    getHuman(_, { id }) {
      const human = readFromDb(id);
      // {
      //   id: id,
      //   age: 26,
      //   height: 123,
      // }
      return human;
    },
    Human: {
      friends({ id }) {
        const friends = friendsOf(id);
        // [{id: 'friend-1-id'}, {id: 'friend-2-id'}, ...]
        return friends;
      },
    },
  },
};

However, if the schema defines getHuman: Human!, then the typescript-resolvers will set the type of the getHuman resolver as a function that must return an object that has a friends,

export type Human = {
   __typename?: 'Human';
  id: Scalars['ID'];
  age: Scalars['Number'];
  height: Scalars['Number'];
  friends: Array<Human>;
};

Of course, the getHuman resolver purposefully does not return the type above. We're relying on the Human definition to fill in the friends field.

At this point, I don't know how to proceed: TS is rightfully reporting a type mismatch. How do I make this work?

[ardatan]

Actually GraphQL in general allows you to return any kind of data in resolvers. So that's why we have mappers to let specify the types for those.
https://graphql-code-generator.com/docs/plugins/typescript-resolvers#mappers---overwrite-parents-and-resolved-values

[aryzing]

Spot on, thanks @ardatan !

[dotansimha]

@aryzing I've just wrote a short tutorial for using mappers, you might find this helpful :) https://the-guild.dev/blog/better-type-safety-for-resolvers-with-graphql-codegen

[loucadufault]

Any chance of making the tutorial usable again (the code examples are dead). Thanks!