TypeScript type LeanDocument for mongoose and nestjs

poc.ts

class Doc {
    attrA: string;
    attrB: string;
    id: string;
    _id: any;
    _v: number;

    func1 = () => {}
    func2 = () => {}
}

class MyDocument extends Doc {
    attrC: string;
    attrD: string;

    _id: string;
}

type LeanDocument<C, P extends {_id: unknown}> = Pick<C, Exclude<keyof C, keyof P>> & Pick<P, Extract<keyof P, "id" | "_v">> & {
    _id: C extends { _id: unknown } ? C['_id'] : P['_id'];
};

const myDoc:MyDocument = new MyDocument();
// try typing myDoc. and see that all properties from MyDocument and Doc are available
// myDoc.

const leanDoc:LeanDocument<MyDocument, Doc> = myDoc;
// Now try typing excluded. The only proerties available are attrC, attrD, id, _id and _v
// leanDoc.

usage.ts

import { Model, Document } from 'mongoose';

export type LeanDocument<C extends Document, P extends Document> = Pick<
  C, // pick keys from C i.e. User provided document object
  Exclude<keyof C, keyof P> // Remove all attributes and methods coming from Document
> &
  Pick<P, Extract<keyof P, 'id' | '_v'>> & {
    // Above: extract and pick id (which is a virtual prop) & _v from Document
    _id: C extends { _id: unknown } ? C['_id'] : P['_id']; // Use user-provided custom _id if available
  };
  
  //...
  //...
  
  export abstract class BaseService<T extends Document> {
  constructor(protected readonly _model: Model<T>) {}

  protected toObject(doc: T): object {
    return doc.toObject({ virtuals: true, getters: true });
  }

  async findAll(query): Promise<LeanDocument<T, Document>[]> {
    return this.findDocuments(query).then((docs) =>
      docs.map(this.toObject.bind(this))
    );
  }