Exposing an array of object using class-transformer

Question

I am not able to expose an array of objects. The Followers array is not getting exposed, even though I exposed in the UserDto

this is what I am getting,

{
    "id": "5ff4ec30-d3f4-43d3-b5ad-82b03e1c5481",
    "userName": "jdbfjl",
    "email": "jdfbaj@gmail.com",
    "bio": "Duuude",
    "avatar": "sjldflaeulajsnlnaefb",
    "followerCount": 0,
    "followeeCount": 0,
    "verified": false,
    "followers": [
      {},
      {},
      {}
    ],
    "followees": [
      {}
    ]
  }

and expected is like

{
    "id": "5ff4ec30-d3f4-43d3-b5ad-82b03e1c5481",
    "createdAt": "2021-08-11T11:07:11.688Z",
    "updatedAt": "2021-08-11T11:07:11.688Z",
    "userName": "ashdviah",
    "email": "hsdvhas@gmail.com",
    "bio": "I am Handsome",
    "avatar": "sjldflaeulajsnlnaefb",
    "followerCount": 0,
    "followeeCount": 0,
    "verified": false,
    "followers": [
      {
        "id": "db1d30c6-5607-4d87-8838-69f906c3c44e",
        "createdAt": "2021-08-11T11:09:33.018Z",
        "updatedAt": "2021-08-11T11:09:33.018Z"
      },
      {
        "id": "31492cd6-7c56-48f6-aff3-792a980b5100",
        "createdAt": "2021-08-11T11:11:01.288Z",
        "updatedAt": "2021-08-11T11:11:01.288Z"
      },
    ],
    "followees": [
      {
        "id": "ab095d0d-b9fa-41a4-be35-13fe9dd6f7a1",
        "createdAt": "2021-08-11T12:55:18.139Z",
        "updatedAt": "2021-08-11T12:55:18.139Z"
      }
    ]
  }

I am getting this output when I am not specifying interceptor to that route... But it turns out that I am exposing password entry with it...

my current approach is something like this : which is not working as expected... what am i missing here ?

class mock {
  @Expose() id : string;
  @Expose() createdAt : Date;
  @Expose() updatedAt : Date;
}

export class UserDto {
  @Expose()
  id : string;
  
  @Expose()
  userName : string;
  
  @Expose()
  email : string;

  @Expose()
  bio : string;

  @Expose()
  avatar : string;

  @Expose()
  followerCount : number;

  @Expose()
  followeeCount : number;

  @Expose()
  verified : boolean;

  @Expose()
  followers : Array<mock>;

  @Expose()
  followees : Array<mock>;
}

And transform is getting done by one interceptor that I used at the controller.

usage : @Serialize(UserDto) decorator

export function Serialize(dto: ClassConstructor) {
  return UseInterceptors(new Serializeinterceptor(dto));
}

export class Serializeinterceptor implements NestInterceptor {
  constructor(private dto: any) {}

  intercept(context: ExecutionContext, handler: CallHandler) {
    return handler.handle().pipe(
      map((data: any) => {
        return plainToClass(this.dto, data, {
          excludeExtraneousValues: true,
        });
      }),
    );
  }
}

Answer 1

For types that are not primitives (i.e. classes) you need to add the @Type(() => ClassType) decorator, so that class-transformer can know what it's supposed to do about the non-primitive. In this case, you need @Type(() => mock).

This is also necessary according to their docs, for any arrays.