Question

I am developing a simple forum web application using SpringMVC, JPA2.
I have created JPA entities like User, Forum, Post etc which reflects the DB table structure.

But while displaying the data on UI I need DTOs as I can’t always hold the data to be displayed on UI using Entities.

For ex: Change Password screen. Here I need to hold Old Pwd, New Password and Confirm New Pwd. But User entity won’t have Old/New/Confirm Pwd fields, it just has Password. So I need to create DTOs which are just data carriers between Web and service layers.

My question is while creating DTO objects, should I put all the properties in DTO itself or wrap the Entity in DTO and add additional properties needed?

Ex: For Edit User Screen,

public class UserDTO
{
     private User user; // User is a JPA entity
     // setters & getters
}

With this I can pass the underlying User entity to my service layer. But while binding UI properties to DTO I need to associate PropertyEditors.

(or)

public class UserDTO
{
    private String userId;
    private String userName;
    private String password;
    // setters & getters
}

With this approach, I need to convert & copy the DTO properties into JPA entities and pass to Service layer.

Which approach is better? Or is there any other approach without DTOs altogether?

Answer 1

Your first approach still carries the Entity object itself to the presentation layer. If you have additional parameters that are not coming from the database, and your persistence context is still available, then this approach is sufficient.

The second approach requires duplication of code, which is not ideal.

If the persistence context is not available, I would suggest detaching the Entity from the persistence context using EntityManager.detach(), rather than creating a parallel hierarchy of beans.

On the other hand, if data is coming in from the presentation layer, you will need to load the Entity from the database (using find() or something similar) and update it, or merge() it into the persistence context.