EmbeddedId with Generated field value

I know the following 2 ways to declare a composite Primary key:

********* Solution 1 *********

@Entity @IdClass(CompositePK.class) public class A {
    @Id private long uid;
    @Id private String zone;
}

public class CompositePK {
    private long uid;
    private String zone;
}

********* Solution 2 *********

@Entity public class A {

@EmbeddedId private CompositePK pk;
}

@Embeddable public class CompositePK {
    private long uid;
    private String zone;
}

In both solutions I expected I could get a generated value for the field uid by simply adding the documented annotation @GeneratedValue like the following:

Solution 1) class A { @Id @GeneratedValue private long uid; ... }

Solution 2) class CompositePK { @GeneratedValue private long uid; ... }

Actually I have several Entity classes (A, B, C, D, etc.) using the same CompositePK, so I'd prefer Solution 2 to have a more compact coding. But unfortunately the only working one is Solution 1.

Is this an issue or simply a not contemplated future?

Automatic generated IDs is currently supported only for entity objects (and not for embeddable classes).

Consider using:

@IdClass(ZoneId.class)
@Entity public static class A {
    @Id @GeneratedValue public long id;
    @Id public String zone;
}

public static class ZoneId {
    public long id;
    public String zone;
}

Okay, I'm going to fill all my classes with redundant fields and their relative getters and setters. 

But at this point has ZoneId class (or CompositePK class) to be declared as @Embeddable static class with annotated fields? I believe declaring it like the following should be the same:

public class ZoneId {
    public long id;
    public String zone;
}

Do you advise differently?

Thank you

You are right. Annotations are not required in the ID class and the example above was fixed accordingly.

Maybe you can inherit the common IDs from a common super entity class / mapped superclass.

It's a good suggestion. But this way how objectDB would count each object instances? Would it be 1 or 2 units for each derived object? I wouldn't exceed the 1 million limit ...

Thank you

Every object is count once even if it is an instance of a class with a deep inheritance.

Perfect. Then I can proceed this way. 

Many thanks and regards.