How to use different model and gql types?

[bennyk8y]

Hi!
Assuming this graphql schema:

type GQLUser {
  fullName: String
}

type Query {
  getUser(args: Args): GQLUser
}

I have a case that there is a query resolver with this shape:

Query: {
   getUser: (parents, args) => db.readUser(args); // <-- Error #1
  }

and assuming the db model looks like

interface DBUser {
  name: string
}

And i want to use chained resolver this way:

GQLUser: {
     fullName: (parent) => parent.name  // <-- Error #2
}

so the end result of resolvers looks like:

import { Resolvers } from '__generated__';
const resolvers: Resolvers = {
  GQLUser: {
       fullName: (parent) => parent.name  // <-- Error #2
   },
  Query: {
     getUser: (parents, args) => db.readUser(args); // <-- Error #1
  }
};

As noted in the code, it raises 2 problems:

1. (error No' 1) The returned value of getUser is DBUser but in the schema (and in the generated types) is GQLUser. Codegen is not aware the there is a chained resolver that will transform DBUser result to the correct GQLUser type.
2. (error No' 2) The parent type in the resolver of fullName is GQLUser but i need it to be DBUser because this is what is being returned from getUser.

Tried to solve it by setting allowParentTypeOverride: true :

import { UserResolvers, Resolvers } from '__generated__';

const userResolvers: UserResolvers<Context, DBUser> = {
   GQLUser: {
       fullName: (parent) => parent.name // <-- now it works
   }
};

const resolvers: Resolvers = {
  GQLUser: userResolvers, // <-- now this fails with Type 'UserResolvers<Context, DBUser>' is not assignable to type 'UserResolver<Context, GQLUser> | undefined'
   Query: {
     getUser: (parents, args) => db.readUser(args); // <-- still Error #1
   }
};

Adding a mapper from GQLUser to DBUser wont help because i want to return GQLUser from getUser resolver

is there a way to solve these issues?

[bennyk8y]

After reading this: https://the-guild.dev/blog/better-type-safety-for-resolvers-with-graphql-codegen
i would like to add that the reason that i don't want to use mapper is because the GQLUser resolver will be omitted there wont be any TS error but clearly the return value of getUser would be wrong and gql will fail at runtime (because nothing will transform DBUser to GQLUser) and that's what im trying to avoid.

[gilgardosh]

I'm not sure I fully understand your issue, and the need of avoiding mappers.
I think this video examples it well