Type is incorrect for Query.distinct when field is a nested field

[bpabel]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.1.2

Node.js version

18.x

MongoDB server version

4.2.8

Typescript version (if applicable)

No response

Description

When using the distinct query for nested fields, the declared type of the return value is unknown[], even though the type should be statically discoverable as string[].

A minimal example

myrecord.schema.ts

import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
import { Document } from 'mongoose';


@Schema()
export class Foo {
  @Prop()
  one: string;
}

export const FooSchema = SchemaFactory.createForClass(Foo);


@Schema()
export class MyRecord extends Document {

  @Prop()
  _id: string;

  @Prop({ type: FooSchema })
  foo: Foo;

export const MyRecordSchema = SchemaFactory.createForClass(MyRecord);

myrecord.service.ts

import { Injectable } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model } from 'mongoose';
import { MyRecord } from '../schemas/myrecord.schema';

@Injectable()
export class MyService {
  constructor(
    @InjectModel('myrecord') private model: Model<MyRecord>,
  ) {}

  async myQuery(): Promise<void> {
    const foos: string[] = await this.model.distinct('foo.one').exec()
  }

}

The type checking error shows:

Type 'unknown[]' is not assignable to type 'string[]'

Steps to Reproduce

I've included some sample code above. It's written in the style of nestjs, so it may need to be modified a bit for a simpler use case without nestjs.

1. Create a document schema with a subdocument.
2. Write a distinct query for the document on one of the nested fields on the subdocument.
3. The specified return type will be unknown[]

Expected Behavior

The resolved return type should be an array of the subdocument field type. In this case, string[].

[vkarpov15]

Confirmed that this is an issue. We'll investigate and see if we can fix this. In the meantime, you can add a type override as follows to prevent this compiler error.

const foos: string[] = await this.model.distinct<'foo.one', string>('foo.one').exec()