Problem:

I want to get all user data from populate, but it is not populated the data with 1:1 relationship between User and Player model.

Schemas are simplified.

User schema:

export interface IUser {
  _id: string;
  name: string;
  surname: string;
  avatar: string;
  age: number;
  email: string;
  password: string;
  roles: (typeof ObjectId)[]; // loaded ok
}

const transform = (doc, ret, options) => {
  ret.id = ret._id;
  delete ret._id;
  delete ret.password;
  delete ret.roles;
  return ret;
};

@Schema({
  versionKey: false,
  toObject: {
    transform,
  },
  toJSON: {
    transform,
  },
})
export class User implements IUser {
  @ApiProperty()
  @Prop({
    default: randomUUID,
    type: UUID,
    required: true,
    transform: (id: any) => id.toString(),
  })
  _id: string;

  ...

  @ApiProperty()
  @Prop({
    type: [
      {
        type: ObjectId,
        ref: Role.name,
        required: true,
      },
    ],
  })
  roles: (typeof ObjectId)[]; // Works fine
}

Player schema:

export interface IPlayer {
  nickname: string;
  user: typeof UUID;
}

// To convert _id to id
const transform = (doc, ret, options) => {
   ret.id = ret._id;
   delete ret._id;
   delete ret._gen;
   return ret;
}

@Schema({
  versionKey: '_gen',
  toObject: {
    transform
  },
  toJSON: {
    transform
  },
})
export class Player implements IPlayer {
  @ApiProperty()
  @Prop({
    type: String,
    index: true,
    required: true,
  })
  nickname: string;

  @ApiProperty()
  @Prop({
    type: {
      type: UUID,
      ref: User.name,
      required: true,
      unique: true,
    },
  })
  user: typeof UUID;
}

export const PlayerSchema = SchemaFactory.createForClass(Player);

Players service

@Injectable()
export class PlayersService {
  constructor(
    @InjectModel(Player.name)
    private playerModel: Model<IPlayer>,
  ) {}

  async find(): Promise<IPlayer[]> {
    return await this.playerModel
      .find({
        _id: '658ddee2f71a72e6d8ea9698', // just for testing to find specific player
      })
      .populate('user')
      .exec();
  }

Players controller

@ApiTags('player')
@Controller('players')
export class PlayersController {
  constructor(private playersService: PlayersService) {}

  @Get()
  async find(@Res() res: Response) {
    const players = await this.playersService.find();
    return res.json(players);
  }
}

With this configuration my result is:

❌ As you see, user is not populated. User prop has UUID as string (it equals to new UUID(b21439b9-87ff-4646-b9e1-780797c887e8).toString())

[
  {
    "id": "658ddee2f71a72e6d8ea9698"
    "nickname": "nickname",
    "user": "b21439b9-87ff-4646-b9e1-780797c887e8",
  }
]

Then I tried to do same as I did with user-roles relationships (that are work fine).

Changes in Player Schema:

type is an array

transform function to get first elem from the array

...
  @ApiProperty()
  @Prop({
    type: [
      {
        type: UUID,
        ref: User.name,
        required: true,
        unique: true,
      },
    ],
    transform: (docs) => docs.at(0),
  })
  user: typeof UUID;
...

✅ Not it works, but it is mostly workaround than a proper way and would be nice to avoid it

[
  {
    "id": "658ddee2f71a72e6d8ea9698"
    "nickname": "nickname",
    ...
    "user": {
      "id": "b21439b9-87ff-4646-b9e1-780797c887e8"
      "email": "[email protected]"
    },

  }
]

Wishes

I want to describe Prop without array and transform function as in code below and get data directly

@ApiProperty()
  @Prop({
    type: {
      type: UUID,
      ref: User.name,
      required: true,
      unique: true,
    },
  })
  user: typeof UUID;