class serialization not working in nestjs

I've a simple user model and i want to exclude password from it. Using the official docs and answer here i've tried to make it work but this doesn't seem to work as i get a response something like this.

[
  {
    "$__": {
      "strictMode": true,
      "selected": {},
      "getters": {},
      "_id": {
        "_bsontype": "ObjectID",
        "id": {
          "type": "Buffer",
          "data": [
            94,
            19,
            73,
            179,
            3,
            138,
            216,
            246,
            182,
            234,
            62,
            37
          ]
        }
      },
      "wasPopulated": false,
      "activePaths": {
        "paths": {
          "password": "init",
          "email": "init",
          "name": "init",
          "_id": "init",
          "__v": "init"
        },
        "states": {
          "ignore": {},
          "default": {},
          "init": {
            "_id": true,
            "name": true,
            "email": true,
            "password": true,
            "__v": true
          },
          "modify": {},
          "require": {}
        },
        "stateNames": [
          "require",
          "modify",
          "init",
          "default",
          "ignore"
        ]
      },
      "pathsToScopes": {},
      "cachedRequired": {},
      "session": null,
      "$setCalled": [],
      "emitter": {
        "_events": {},
        "_eventsCount": 0,
        "_maxListeners": 0
      },
      "$options": {
        "skipId": true,
        "isNew": false,
        "willInit": true
      }
    },
    "isNew": false,
    "_doc": {
      "_id": {
        "_bsontype": "ObjectID",
        "id": {
          "type": "Buffer",
          "data": [
            94,
            19,
            73,
            179,
            3,
            138,
            216,
            246,
            182,
            234,
            62,
            37
          ]
        }
      },
      "name": "Kamran",
      "email": "kamran@example.com",
      "password": "Pass1234",
      "__v": 0
    },
    "$locals": {},
    "$init": true
  }
]

Here's my model. I'm using Typegoose but the same is the case with Mongoose as well.

export class User extends Typegoose {
  @Transform((value) => value.toString(), { toPlainOnly: true })
  _id: string;

  @prop({ required: true })
  public name!: string;

  @prop({ required: true })
  public email!: string;

  @Exclude({ toPlainOnly: true })
  @prop({ required: true })
  public password!: string;
}

My user service

@Injectable()
export class UserService {
  constructor(@InjectModel(User) private readonly user: ReturnModelType<typeof User>) {}

  async getUsers() {
    return this.user.find().exec();
  }
}

and user controller

@Controller('users')
@UseInterceptors(ClassSerializerInterceptor)
export class UserController {
  constructor(private readonly userService: UserService) {}

  @Get()
  async index() : Promise<User[] | []> {
    return this.userService.getUsers();
  }
}

I tried to use my custom interceptor as described here but that didn't work so i changed it to below code as given here

@Injectable()
export class TransformInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(map(data => classToPlain(this.transform(data))));
  }

  transform(data) {
    const transformObject = (obj) => {
      const result = obj.toObject();
      const classProto = Object.getPrototypeOf(new User());
      Object.setPrototypeOf(result, classProto);
      return result;
    }

    return Array.isArray(data) ? data.map(obj => transformObject(obj)) : transformObject(data);
  }
}

Now it's working but the code is not generic. Any way to make it generic?

I think i've identified the problem but not sure why this happens yet. So here's the problem if i return the instance of the class then the serialization works but if i just return plain db response then the above mentioned issue occurs. So what i did is i updated the prototype of the response objects in the transform method of toObject to my user class. Here's the code.

User Model

@modelOptions({
  schemaOptions: {
    toObject: {
      transform: function(doc, ret, options) {
        Object.setPrototypeOf(ret, Object.getPrototypeOf(new User()));
      }
    },
  },
})
export class User {
  @Transform((value) => value.toString(), { toPlainOnly: true })
  public _id: string;

  @prop({ required: true })
  public name!: string;

  @prop({ required: true })
  public email!: string;

  @Exclude({ toPlainOnly: true })
  @prop({ required: true })
  public password!: string;
}

TransformInterceptor

@Injectable()
export class TransformInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(map(data => classToPlain(this.transform(data))));
  }

  transform(data) {
    return Array.isArray(data) ? data.map(obj => obj.toObject()) : data.toObject();
  }
}

And now if you just decorate your controller or method with @UseInterceptors(TransformInterceptor) it will work perfectly. This is a typegoose solution but it will work the same way with mongoose as well.