I'm new to Hibernate and JPA and have a few questions, in order of priority.

1) I have two properties/columns (not sure on the right terminology) that I want to make unique together. How do I do this without nested annotations?

2) What exactly is does MapKey do? How does it work?

3) If I define a ManyToOne relationship, why should I define a OneToMany on the other end?

Thanks,
Bradford

1) What do you mean with nested annotations? It is possible:
Do you mean @UniqueConstraint as nested annotation? If yes, why do you want to do it without it?

2)You can use MapKey to define the key of a Map, where the MapKey relates to the property (of the map's value-entity) to be used as key.

3) It's not mandatory to make an association bidirectional, though it's recommended. So you can keep your ManyToOne without your OneToMany on the other side.

No, it's not!

http://in.relation.to/Bloggers/PersistentCollectionsAreAFeature

Thanks for the quick replies.

I'm trying to use JPA and Hibernate in Scala. Currently, it does not support nested annotations, so the following will not work:

@Table(name="tbl_sky",
uniqueConstraints = {@UniqueConstraint(columnNames={"month", "day"})}
)

I was wondering if I could define this in some XML file. If so, which XML file?

Thanks

You can override annotations using xml.

Probably the easiest way would be placing a file orm.xml in your META-INF folder, where persistence.xml is placed. This file gets read automatically.

If you need more information on how to map via xml, see the reference guide.