Parsing: Entity Classes to DTO

Question

I'm building a GWT application for GAE, using JDO for Datastore access. I use and Entity class for data mapping, so it contains lots of Persistence annotations:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class AppointmentEntity implements Serializable {
 private static final long serialVersionUID = 1L;
 @PrimaryKey
 @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
 private Long id;
 @Persistent
 private String firstName;
 @Persistent
 private String lastName;
 @Persistent
 private String DNI;
 @Persistent
 private Date appointmentDate;
 @Persistent
 private String attendant;
 @Persistent
 private String treatment;
 @Persistent
 private String details;
 @Persistent
 private Date nextAppointment;
 @Persistent(serialized = "true")
 private DownloadableFile file;
 //getters and setters...

Because of GWT and JDO nature, i can't use this Entity classes in my presentation layer; so there's a need of passing Entity Object attributes to the corresponding DTO, which is a POJO that has the same attributes of the Entity class:

public class AppointmentDTO implements Serializable {
 private static final long serialVersionUID = 1L;
 private Long id;
 private String firstName;
 private String lastName;
 private String DNI;
 private Date appointmentDate;
 private Date nextAppointmentDate;
 private String attendant;
 private String treatment;
 private String details;
 //getters and setters...

To do the Job of mapping attributes i make a Wrapper class that handles it, but it doesn't feel quite right to me. Does anyone have a better approach?

public class AppointmentWrapper {
 private List<AppointmentEntity> entitiesList;
 public AppointmentWrapper(List<AppointmentEntity> appointmentEntities) {
 entitiesList = appointmentEntities;
 }
 public List<AppointmentDTO> getDTOList() {
 List<AppointmentDTO> dtoList = new ArrayList<AppointmentDTO>();
 for (AppointmentEntity entity : entitiesList) {
 AppointmentDTO dto = new AppointmentDTO();
 dto.setId(entity.getId());
 dto.setFirstName(entity.getFirstName());
 dto.setLastName(entity.getLastName());
 dto.setAppointmentDate(entity.getAppointmentDate());
 dto.setNextAppointmentDate(entity.getNextAppointment());
 dto.setAttendant(entity.getAttendant());
 dto.setDetails(entity.getDetails());
 dto.setDNI(entity.getDNI());
 dto.setTreatment(entity.getTreatment());
 dtoList.add(dto);
 }
 return dtoList;
 }
}

• Quentin Pradet: My feeling is that few members have GWT/JDO experience, but lot of them have design/programming experience. Linking to what Entity or DTO are would probably help everyone understand the issue in order to help you.
• Carlos Gavidia-Calderon: As request, i'm included full classes source code. It's not a GWT/JDO problem, is more a design issue
• Apprentice Queue: Solutions to design issues are frequently dependent on the technology being used.

Answer 1

There is this concerning GWT and GAE objects. If that doesn't work for you, I would rather have a class of public static methods that does the conversions rather than sticking it into some kind of "wrapper class" that contains object states. For example,

public final class JDOEntityUtil {
 static public AppointmentDTO toDTO(AppointmentEntity entity) {
 AppointmentDTO dto = new AppointmentDTO();
 dto.setId(entity.getId());
 dto.setFirstName(entity.getFirstName());
 dto.setLastName(entity.getLastName());
 dto.setAppointmentDate(entity.getAppointmentDate());
 dto.setNextAppointmentDate(entity.getNextAppointment());
 dto.setAttendant(entity.getAttendant());
 dto.setDetails(entity.getDetails());
 dto.setDNI(entity.getDNI());
 dto.setTreatment(entity.getTreatment());
 return dto;
 }
 static public AppointmentEntity toEntity(AppointmentDTO dto) {
 AppointmentEntity entity = new AppointmentEntity();
 entity.setId(dto.getId()); /* or however you want to construct this */
 entity.setFirstName(dto.getFirstName());
 entity.setLastName(dto.getLastName());
 entity.setAppointmentDate(dto.getAppointmentDate());
 entity.setNextAppointmentDate(dto.getNextAppointment());
 entity.setAttendant(dto.getAttendant());
 entity.setDetails(dto.getDetails());
 entity.setDNI(dto.getDNI());
 entity.setTreatment(dto.getTreatment());
 return entity;
 }
}