Question

What will actually happen if I provide a full set of annotations for JPA and JDO on data objects?

Can I then switch between them without touching the code? how can I switch what to aplay external configuration files? I know in the META-INF there are persistence.xml jdoconfig.xml but I do not understand the how to use them. (may be a link to a compressive explanation?)
Currently I got both files in place and the code below compiles Ok. I am interested in what goes under the hood to understand implications of this approach.

For vivid example:

@Entity
@PersistenceCapable(identityType = IdentityType.APPLICATION, detachable = "true")
class B
{
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private Long   id;

    @Persistent
    @Basic
    private String name;
}

Platform: default setup of Google AppEngine 1.4 it uses DataNucleus Enhancer (version 1.1.4)

Answer 1

Although I have never try this it should work. This is the point of annotations: the do not affect the code unless they are used. JPA implementation uses its annotations, JDO uses others.