Adding some thoughts from discussions via ML and IRC.
It would be nice if there was a way for the user to declare custom generator annotations such as {{@CreationTimestamp}}. Such a _generator annotation type_ might be defined like this:
{code}
@Generated(
when = INSERT,
generator = MyCreationTimestampGenerator.class
}
@Target({ METHOD, FIELD})
@Retention(RUNTIME)
public @interface MyCreationTimestamp {
TemporalType type();
String source default "vm";
}
{code}
Here the {{@Generated}} annotation is used to mark {{@MyCreationTimestamp}} as custom generator annotation type, specifying the generator type and when to invoke it. A custom generator annotation may define additional attributes as suited per its requirements.
The generator of such an annotation would implement a specialized contract which receives the annotation instance upon initalization:
{code}
public interface CustomDynamicValueGenerator<V, A extends Annotation> extends DynamicValueGenerator<V> {
void initialize(A generatorAnnotation);
}
{code}
{code}
public class MyCreationTimestampGenerator implements DynamicValueGenerator<String, MyCreationTimestamp> {
TemporalType type;
void initialize(MyCreationTimestamp annotation) {
this.type = annotation.type();
}
String generateValue(Session session, Object owner) {
//...
}
}
{code}
Thinking about it some more, when given on a custom generator annotation type, {{@Generated#generator()}} should only accept a {{CustomDynamicValueGenerator}} type, so having a special annotation might be the better idea.
Optionally it might also make sense to allow for specifying the time of execution for custom generators:
{code}
@Modifier(when={INSERT, UPDATE})
private String lastModifier;
{code}
Unfortunately one can't define a contract for annotation types by means of an interface, so one could only declare a naming convention for this method.
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