Model Mapper - using custom methods

Question

A springboot project where I need to construct a DTO for a dashboard view using nominated fields from the parent and nominated fields from the newest of each of the children.

The entities are Plane which has a OneToMany relationship with Transponder, Maint Check and Transmitter.

Plane

@Entity
@Data
public class Plane {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    private Long id;
    private String registration;
    @JsonIgnore
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "plane")
    private List<Transponder> listTransponder = new ArrayList<>();
    @JsonIgnore
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "plane")
    private List<Transmitter> listTransmitter = new ArrayList<>();
    @JsonIgnore
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "plane")
    private List<MaintCheck> listMaintCheck = new ArrayList<>();

Transponder

@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Transponder {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    private Long id;
    private String code;
    private LocalDate dateInserted;
    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    private Plane plane;
}

Maint Check and Transmitter have similar entities with a LocalDate field.

PlaneDTO looks liike

@Data
public class PlaneDTO {
private String registration;
private LocalDate maintCheck;      // date of most recent Maint Check
private String transponderCode;    // string of most recent Transponder code 
private Integer channel;           // Intger of most recent Transmitter Freq     
}

I have attempted to consruct this PlaneDTO in the service layer, but I am manually doing much of the sorting of the lists of Transponder, Transmitter and Maint Check to get the most recent record from these lists.

//DRAFT METHOD CONSTRUCT DTO
@Override
public PlaneSummaryDTO getPlaneSummaryDTOById(Long id) {
  Plane Plane = this.get(id);
  PlaneSummaryDTO PlaneSummaryDTO = new PlaneSummaryDTO();
    ModelMapper mapper = new ModelMapper();
    PlaneSummaryDTO = modelMapper.map(get(id), PlaneSummaryDTO.class);
    PlaneSummaryDTO.setTRANSPONDERCode(getNewestTRANSPONDERCode(Plane));
    PlaneSummaryDTO.setLastMaintCheck(getNewestMaintCheckDate(Plane));
    PlaneSummaryDTO.setChannel(getTransmitterCode(Plane));
    PlaneSummaryDTO.setChannelOffset(getTransmitterOffset(Plane));
    return PlaneSummaryDTO;
}

// RETURN NEWEST DATE OF MAINT CHECK BY CATCH DATE
public LocalDate getNewestMaintCheckDate(Plane Plane) {
    List<MaintCheck> listMaintCheck = new ArrayList<>(Plane.getListMaintCheck());
    MaintCheck newest = listMaintCheck.stream().max(Comparator.comparing(MaintCheck::getCatchDate)).get();
    return newest.getCatchDate();
}

// RETURN NEWEST TRANSPONDER CODE FROM Plane BY DATE INSERTED
public String getNewestTransponderCode(Plane Plane) {
    List<Transponder> listTransponder = new ArrayList<>(Plane.getListTransponder());
    Transponder newest = listTransponder.stream().max(Comparator.comparing(Transponder::getDateInserted)).get();
    return newest.getCode();
}

// OTHER METHODS TO GET MOST RECENT RECORD

QUESTION Is there a better way to calculate the most recent record of the child, using model mapper more efficiently (custom method?)

I am open to changing to MapStruct if it better supports getting the most recent child.

Answer 1

So here's a different approach to the data model. I'll be using Transponder because the others are analog.

The target domain model could look like this:

@Data
class Plane {
 Long id;
 String registration;
 Transponder activeTransponder;
}
@Data
class Transponder {
 Long id;
 Integer code; // this is a 4-digit octal number, why String? your call though
 Long planeId; 
 Instant assignStart;
 Instant assignEnd;
}

In the database, it would be sufficient to store the id and registration for the plane, because you can determine the current transponder with a proper query on the db entity, eg where transponder.planeId=id and transponder.assignEnd IS NULL. You can also store the transponderId of course, but then you'd need to take care to keep the data consistent between the tables.

If you want a history of all transponders - which to me seems like an entirely different use case to me, you can easily retrieve it in a separate service with a query getTransponderHistoryByPlane(long planeId) with a query like from transponders t where t.planeId=$planeId sorted by t.assignStart.

Again, this does depend on your use cases, and assumes that you usually only need one transponder for a given plane except in special cases, like from a different endpoint.

Anyway, this were my thoughts on the domain model, and you were aiming for your Dto; however, this is then easily mapped with mapstruct like (assuming you do the same for maintCheck and transmitter)

@Mapper
interface PlaneDtoMapper {
  @Mapping(target = "transponderCode", source = "transponder.code")
  @Mapping(target = "maintCheck", source = "maintCheck.date")
  @Mapping(target = "channel", source = "transmitter.channel")
  PlaneDTO fromPlane(Plane p);
}

You don't need the "registration" mapping because the fields in plane and dto are the same, and the @Mapping annotations tell mapstruct which subfields of which fields of plane to use.

Answer 2

I briefly used ModelMapper in the past. I would suggest using mapstruct since I personaly find it easier to use. I know your mapping can be done there ;). In Mapstruct your Mapper could look something like this:

@MapperConfig(
        componentModel = "spring",
        builder = @Builder(disableBuilder = true)
)
public interface PlaneMapper {

    @Mapping(target = "lastMaintCheck", ignore = true)
    PlaneDTO planeToPlaneDTO(Plane plane);

    @AfterMapping
    default void customCodePlaneMapping(Plane source, @MappingTarget PlaneDTO target) {
        target.setLastMaintCheck(source.getListMaintCheck.stream().max(Comparator.comparing(Transponder::getDateInserted)).get())
   }

Your mapper call would then only be one line:

@Service
@RequiuredArgsConstructor
public class someService{

    private final PlaneMapper planeMapper;

    public void someMethod(){
        ....
        PlaneDTO yourMappedPlaneDTO = planeMapper.planeToPlaneDTO(plane);
        ....
    }

I did not fill in all values. But i hope the concept is clear.

EDIT:

You would also have to add the dependency of "mapstruct-processor" so that the MapperImpl classes can be gererated.

    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct-processor</artifactId>
        <version>${org.mapstruct.version}</version>
        <scope>provided</scope>
        <optional>true</optional>
    </dependency>