I have this ProgramDto : ```data class ProgramDto(...

# spring

[dany giguere]

I have this ProgramDto :

data class ProgramDto(
    val id: Long?,
    val title: String,
    val description: String,
    var images: List<ImageDto>? = emptyList()
)

that may (or not) have Sessions. Sometime the Front end needs it, sometimes it doesn’t. So I’ve created another Dto called ProgramWithSessionsDto. And then I added this function in ProgramDto that converts the ProgramDto to a ProgramWithSessionsDto:

fun ProgramDto.toProgramWithSessionsDto(): ProgramWithSessionsDto = ProgramWithSessionsDto(
    id = id,...

ProgramWithSessionsDto, is this:

data class ProgramWithSessionsDto(
    val id: Long?,
    val title: String,
    val description: String,
    var images: List<ImageDto>? = emptyList(),
    var sessions: List<SessionDto>? = emptyList()
)

But that’s a lot of Dtos I’m going to add to my project. Is there anyway I could simply add this to my ProgramDto:

var sessions: List<SessionDto>? = emptyList(),

but not return it (the sessions) if I don’t need to ? and then I could get rid of ProgramWithSessionsDto.

[Raimund Klein]

Have you thought of composition over inheritance? Assuming you're using Jackson, you could make use of @JsonUnwrapped.

[dany giguere]

I’m not aware that I’m using Jackson. I believe I need to add it as a dependency. using @JsonUnwrapped does it mean the sessions key won’t even be included in the json ?

[Raimund Klein]

In this model, you'd keep the two DTO classes, but ProgramWithSessionsDto would contain a ProgramDto rather than the individual attributes. If you then add @JsonUnwrapped, the JSON structure would look the same as now.

[dany giguere]

ok thanks @Raimund Klein I’ll give it a try 🙂

[Riccardo Lippolis]

alternatively, you could annotate the class with @JsonInclude(JsonInclude.Include.NON_EMPTY), which means that only non-null and non-empty fields will end up in the json. So if the sessions field contains an empty list, it won't be serialized

[dany giguere]

Thanks @Riccardo Lippolis exaclty what I was looking for 🙂