Mapstruct: mapping collection to object

Question

I have a function like so:

public HousesDTO mapHouses(Set<Home> roles) {
        HousesDTO homes = new HousesDTO();
        List<HouseDTO> dtos = new ArrayList<HouseDTO>();
        for (Home home : homes) {
            HouseDTO dto = new HouseDTO(home.getAddress(), home.getPrice());
            dtos.add(dto);
        }
          homes.setAllHomes(dtos);
          return homes;
        }
        return null;
    }

How can this be done using Mapstruct?

Answer 1

In case your HouseDTO has a parameterless constructor and setters for the values you can do it like this:

@Mapper
public interface HousesMapper {
    default HousesDTO toHouses(Set<Home> homes) {
        HousesDTO housesDTO = new HousesDTO();
        housesDTO.setAllHomes(toHousesList(homes));

        return housesDTO;
    }

    List<HouseDTO> toHousesList(Set<Home> homes);
}

If the HouseDTO only has a constructor that expects the properties than there are three options left:

1. Wait for the MapStruct 1.4 release which will support instantiation by constructors
2. Create a default method where you map from Home to HouseDTO manually
3. Create a Builder, see https://mapstruct.org/documentation/stable/reference/html/#mapping-with-builders