Hibernate version: 3.2.4.sp1
Mapping documents: Using annotations
Name and version of the database you are using: Microsoft SQL Server 2005

I am using Hibernate through JPA and would like to have values for a certain non-key persistent field be automatically generated based on an @GeneratedValue and @TableGenerator. However, it does not work. The value in the concerned column in the database is always 0 (zero) in every row.

Is it really possible to generate values for non-key column using @GeneratedValue? Is there something special to be done to get it working?

A search in the forums gave me http://forum.hibernate.org/viewtopic.php?t=968325, which is interesting but not really specifically about @GeneratedValue.

FWIW, http://www.manning-sandbox.com/thread.jspa?threadID=23932 is another place where I am trying to get some closure on this

Thanks in advance.

I thought @GeneratedValue on a non-primary key means hibernate will do a select after insert to get the field value from database, and it does not mean hibernate will generate a value for it. You should be able to verify this if you see a select the_column from the_table statement after inserts.



Farzad-

I messed up. It's @Generated not @GeneratedValue and in Hibernate documentation @GeneratedValue is always mixed with @Id so it might imply that's the only place it works.



Farzad-

The first line of javadoc for the currently released spec at http://java.sun.com/javaee/5/docs/api/javax/persistence/GeneratedValue.html seems to indicate that @GeneratedValue is specified to ACTUALLY WORK only for key fields.

Oh well, here's hoping that this will be specified to work even for non-key fields in JPA 2.0

Still you can use @Generated and have the database handle this for you.


Farzad-

Farzad,

Using the Hibernate @Generated means telling Hibernate that the databse will generated the value of the concerned field. I have not tried this, but would imagine such a scheme to be non-portable accross databases. It would be great if you could elaborate on what you are eluding to, even if it implies a non-portable scheme of thins.

Thanks.

@Generated tells hibernate that this field gets a value in database and hibernate should fetch its value. Then you could put the generation logic in database. It is pretty much portable since it is only a select; however, I am not sure if all databases have a solution for default values and/or triggers.



Farzad-

Unfortunately, we do not have the freedom of using trigger or it's friends to generate such values. The reason is portability concern. We are developing software of a platform nature and would not want the slightest of portability risks to creep in. And, it's not really a default value we are looking for but rather a value that is unique across the rows. I think, currently, my only option is to implement a Java based identifier value generating scheme(maybe based on java.util.UUID), which is a shame given the presence of JPA and providers such as Hibernate - unless there is way to leverage specific generators in Hibernate such as org.hibernate.id.UUIDHexGenerator in a non-key field context.

I am on the wrong path or a non-ideal path.