How do I create a mapper from entity to dto, where dto is nested?

Issue

Two entities with corresponding dtos are given

entities:

class GalleryBlock(
    var images: List<Image?>,
    override val sortIndex: Int = 0,
) : ArticleBlock(sortIndex)

class Image(
    var url: String,
    var imageSize: ImageSize,
    override var id: Long,
    override var lastModified: Date,
    override var lastModifiedBy: String? = null ) : DBEntity

enum class ImageSize {
    SMALL,
    MEDIUM,
    LARGE, }

dtos

data class GalleryBlockDto(
    var images: List<ImageDto>,
    override val sortIndex: Int,
) : ArticleBlockDto

data class ImageDto(
    var id: Long,
    var url: String,
    var imageSize: ImageSize,
)

for the mapping I have written an interface Mapper

interface Mapper<E, D> {
    fun fromEntity(entity: E): D
}

for the mapping from class Image to ImageDto I have create a class ImageMapper

@Component
class ImageMapper: Mapper<Image, ImageDto> {
    override fun fromEntity(entity: Image): ImageDto {
        return ImageDto(entity.id, entity.url, entity.imageSize)
    }
}

when mapping the GalleryBlock I did the same but I get a type mismatch.

@Component
class GalleryBlockMapper: Mapper<GalleryBlock, GalleryBlockDto> {
    override fun fromEntity(entity: GalleryBlock): GalleryBlockDto {
        val images = entity.images
        val sortIndex = entity.sortIndex
        return GalleryBlockDto(images, sortIndex)
    }
}

is my approach correct? and how do I get the type mismatch fixed without changing the fields of Dto and entities?

Solution

In your GalleryBlockMapper you pass Image instances to the GalleryBlockDto. But ImageDto instances are needed. The ImageMapper needs to be injected into the GalleryBlockMapper, so the images can be mapped.

@Component
class GalleryBlockMapper(private val imageMapper: ImageMapper): Mapper<GalleryBlock, GalleryBlockDto> {
    override fun fromEntity(entity: GalleryBlock): GalleryBlockDto {
        val images = entity.images.map { imageMapper.fromEntity(it) }
        val sortIndex = entity.sortIndex
        return GalleryBlockDto(images, sortIndex)
    }
}

Answered By - user2999226