Is there a pattern for using DTO's without having to duplicate the domain object's properties?

Question

I'd like to use DTO's in my view models in lieu of my domain objects, however I'm having a hard time justifying the maintenance overhead of having to maintain two sets of properties for each domain object.

I was wondering if anyone has implemented or knows of a pattern where the properties of a domain object are separated from the object's actions without having to maintain two sets of properties.

One thought I had would be to have my domain object be only properties and attaching the actions as a subclass:

public class Person{
    private String firstName;
    private String lastName;

    public String getFirstName(){
        return this.firstName;
    }

    public String setFirstName(string firstName){
        this.firstName = firstName;
    }

    ...
}

public class PersonActions extends Person{
    public void save(){
        ...
    }

    public Person get(){

    }
}

This way still feels a bit kludgy as I'd have to pass around a PersonAction class if I wanted a full representation of the domain object.

Answer 1

You could use an interface exposing only your object's data, without any domain methods. You'd still need to maintain two classes, but that would be a lot easier since most of the changes could be refactored by your IDE (Eclipse for example). Here's an example:

public interface PersonView {
    String getFirstName();
    String setFirstName();
}

public void Person implements PersonView {
    private String firstName;

    @Override // This annotation guarantees the interface is correct 
    public String getFirstName() {
        return firstName;
    }

    ...domain methods...
}

Is not a perfect solution, but it's a pretty clean one.

As for the problem itself, I for one don't really mind exposing the whole object to the view layer. IMHO, I don't think hiding some methods is worth the overhead. The team should have the discipline to use the objects wisely, but that's just my opinion.