Hibernate/persistence without @Id

Question

I have a database view thar yields a result set that has no true primary key. I want to use Hibernate/Persistence to map this result set onto Java objects. Of course, because there is no PK, I cannot decorate any field with @Id.

When deploying, Hibernate complains about the missing @Id. How can I work around this?

Answer 1

You could check if there is logic wise an id and provide mapping information accordingly. Hibernate will not check the database for existence of a defined primary key.

Answer 2

For each entity, you must designate at least one of the following:

• one @Id
• multiple @Id and an @IdClass (for a composite primary key)
• @EmbeddedId

so maybe you can create a composite primary key, containing multiple fields?

Answer 3

If there's a combination of columns that makes a row unique, model a primary key class around the combination of columns. If there isn't, you're basically out of luck -- but you should reexamine the design of the view since it probably doesn't make sense.

There are a couple different approaches:

@Entity
public class RegionalArticle implements Serializable {

    @Id
    public RegionalArticlePk getPk() { ... }
}

@Embeddable
public class RegionalArticlePk implements Serializable { ... }

Or:

@Entity
public class RegionalArticle implements Serializable {

    @EmbeddedId
    public RegionalArticlePk getPk() { ... }
}

public class RegionalArticlePk implements Serializable { ... }

The details are here: http://docs.jboss.org/ejb3/app-server/HibernateAnnotations/reference/en/html_single/index.html#d0e1517

Here's an posting that describes a similar issue: http://www.theserverside.com/discussions/thread.tss?thread_id=22638