Gang,
The Chronos development is surfacing some issues about Value Objects, and
their particular nature.
For instance, look at the difference between;
public interface PersonEntity extends EntityComposite, HasName
{}
public interface StreetComposite extends Composite, HasName
{}
and
public interface HasName
{
String getName();
void setName( String name );
}
The issues is that HasName.setName() should exist for the PersonEntity, but
should not exist for the StreetComposite value object, since the VO should be
immutable.
We could do something like;
public interface PersonEntity extends EntityComposite, Nameable
{}
public interface StreetComposite extends Composite, Name
{}
public interface Nameable
{
Name getName();
void setName( Name name );
}
public interface Name
{
String getName();
}
public class NameBean implements Name
{
private String name;
public NameBean( String name )
{
this.name = name;
}
public String getName()
{
return name;
}
}
So that if you want to change the Name of the Person, you would need to do;
Person p = ...
p.setName( new NameBean( "Niclas" ) );
but, retrieval is ugly like nothing else...
Person p = ...
String name = p.getName().getName();
Not sure I like that. We could also separate the setter interface from the
getter interface;
public interface PersonEntity extends EntityComposite, Name, NameSettable
{}
public interface StreetComposite extends Composite, Name
{}
public interface Name
{
String getName();
}
public interface NameSettable
{
void setName( String name );
}
A lot better, but then we would need some form of explicit support in Qi4j
Core that two separate mixins are sharing the same member.
Perhaps we could instead do;
@ImplementedBy( ImmutableName.class )
public interface Name
{
String getName();
}
@ImplementedBy( MutableName.class )
public interface NameSettable extends Name
{
void setName( String name );
}
and rely on that the Mutable implementation would be selected.
Any thoughts??
Cheers
--
Niclas Hedhman, Software Developer
I live here; http://tinyurl.com/2qq9er
I work here; http://tinyurl.com/2ymelc
I relax here; http://tinyurl.com/2cgsug
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