[Suggestion] Small improvement for typed projection

[jansedlon]

Do you want to request a feature or report a bug?
Suggest solution for a feature

What is the current behavior?
Projection is not typed at all

What is the expected behavior?
To be at least somehow typed

Hello. I'd like to propose a small improvement to have typed projection for the simplest cases. Talking about cases where you use findById(id, { something: 1 }), basically you just use 1 or true.

I would change the type definition of find queries to this

findById<
        Project = undefined,
        ResultDoc = Project extends undefined
          ? T
          : {
              [Key in keyof Project]: Project[K] extends 1
                ? T[Key]
                : Project[Key] extends true
                ? T[Key]
                : any;
            }
      >(
        id: any,
        projection?: Project | null,
        options?: QueryOptions | null,
        callback?: Callback<HydratedDocument<
          ResultDoc,
          TMethods,
          TVirtuals
        > | null>
      ): QueryWithHelpers<
        HydratedDocument<ResultDoc, TMethods, TVirtuals> | null,
        HydratedDocument<ResultDoc, TMethods, TVirtuals>,
        TQueryHelpers,
        ResultDoc
      >;

What it does is that if you decide to use the project parameter in find queries and you want to use simple selects, the result type will only include the properties that you selected. If it's not a simple select (eg { something: "$xx" }), it would just return any.

what do you think?

Note: To use 1 instead of true means, that the project object would need to be marked as const.. like this Model.findById(id, { name: 1 } as const)

[vkarpov15]

I like the idea of allowing overriding the return type of a query, but I think the suggested API is not viable because (1) it is backwards breaking, and (2) doesn't support exclusive projections. Better to just allow findById<Pick<User, 'name'>>(id, { name: 1 }).