Resolving auto-generated typescript-mongodb types for GraphQL output

Question

I'm using the typescript-mongodb plugin to graphql-codegen to generate Typescript types for pulling data from MongoDB and outputting it via GraphQL on Node.

My input GraphQL schema looks like this

type User @entity{
    id: ID @id,
    firstName: String @column @map(path: "first_name"),
...

The generated output Typescript types look correct

export type User = {
   __typename?: 'User',
  id?: Maybe<Scalars['ID']>,
  firstName?: Maybe<Scalars['String']>,
...

And the corresponding DB object

export type UserDbObject = {
  _id?: Maybe<String>,
  first_name: Maybe<string>,
...

The problem is when actually sending back the mongo document as a UserDbObject I do not get the fields mapped in the output. I could write a custom resolver that re-maps the fields back to the User type, but that would mean I'm mapping the fields in two different places.

ie I do not get mapped fields from a resolver like this

  userById: async(_root: any, args: QueryUserByIdArgs, _context: any) : Promise<UserDbObject> => {
    const result = await connectDb().then((db) => {
      return db.collection<UserDbObject>('users').findOne({'_id': args.id}).then((doc) => {
        return doc;
      });
    })
    ...
    return result as UserDbObject;
  }
};

Is there a way to use the typescript-mongodb plugin to only have to map these fields in the schema, then use the auto-generated code to resolve them?

Answer 1

You can use mappers feature of codegen to map between your GraphQL types and your models types. See:

• https://graphql-code-generator.com/docs/plugins/typescript-resolvers#mappers---overwrite-parents-and-resolved-values
• https://graphql-code-generator.com/docs/plugins/typescript-resolvers#mappers-object

Since all codegen plugins are independent and not linked together, you should do it manually, something like:

config:
  mappers:
     User: UserDbObject

This will make typescript-resolvers plugin to use UserDbObject at any time (as parent value, or as return value).

If you wish to automate this, you can either use the codegen programmatically ( https://graphql-code-generator.com/docs/getting-started/programmatic-usage ), or you can also create a .js file instead of .yaml file that will create the config section according to your needs.