Mapping Entity-to-DTO (and vice-versa) in Nest.js

Question

I'm building an API with Nest.js and I've been using a mapper to convert the TypeORM entity to a DTO (and vice-versa).

Until now, I've been doing this manually:

 public static async entityToDto(entity: UserEntity): Promise<UserDto> {
    const dto = new UserDto();

    dto.id = entity.id;
    dto.emailAddress = entity.emailAddress;
    dto.firstName = entity.firstName;
    dto.lastName = entity.lastName;
    dto.addressLine1 = entity.addressLine1;
    dto.addressLine2 = entity.addressLine2;
    dto.townCity = entity.townCity;
 
    [...]

    return dto;
  }

In my opinion, this is a nice (albeit inflexible) approach. It explicitly controls which fields are returned to the user. However, I was under the impression that the purpose of a DTO is to have a single place to modify data about something. If I needed to add a field, I'd have to modify both the DTO and the mapper.

It seems to be the convention to have one mapper per entity. However, if I don't want to return, for example, the accountStatus field, I would have to write a new mapper. So I have now multiple mappers which would need to be modified.

I had the idea to write a "universal" mapper which looks at the fields in the DTO, and maps them to the fields in the entity.

I'm relatively new to TypeScript and Nest.js, so I was wondering how others manage this.

Answer 1

I suggest you should try object property map built-in by typescript. Basically, your entity can be map to dto based on the similar property name like below

 public static async entityToDto(entity: UserEntity): Promise<UserDto> {
    const dto : UserDTO = ({
        ...entity,
        additionalProperty: entity.someProperty
    });

    return dto;
  }

Any property that sharing the same name between DTO and Entity will be mapped. It is far more clean and more flexible.