Lists & Sets

All mappers of Mappie define mapper variants for collections. Specifically, for List and Set. When we want to map a property of such a type, we do not want to copy the collection itself, but the elements contained in such a type. We can reference a mapper using the getters forList and forSet defined in each mapper.

Suppose we have the data class Book containing a list of Page

data class Book(val pages: List<Page>)

data class Page(val text: String)

and we have a data class BookDto containing a list of strings

data class BookDto(val pages: List<String>)

We can define a mapping between Book and BookDto by defining two mappers: a mapper for Page to String, which simply gets the text property, and mapper between Book and BookDto using the inner forList mapper of the PageMapper

object PageMapper : ObjectMappie<Page, String>() {
    override fun map(from: Page): String = from.text
}

object BookMapper : ObjectMappie<Book, BookDto>() {
    override fun map(from: Book): BookDto = mapping {
        BookDto::pages fromProperty Book::pages via PageMapper.forList
    }
}