Retrieving auto inc primary key from entity bean (MySQL DB)

Question

Hello,
I searched the forum intensively, but did not find an answer for the following problem.
I've set up an MySQL database "Location" with two fields (ID, Description), ID is my primary key and I've added the AUTO_INCREMENT flag to this field. This works fine, i can add a row in the table with my entity bean "Location" from my session bean :
Location l = new Location();
l.setDescription("at home");
em.persist(l);
and even when I ask this location back from the DB, there is no problem :
Location l = em.find(Location.class,1);
return l.getDescription();
The rows in the table increment nicely. The problem however is, that you don't allways know the ID. So I would like to do the following from my session bean:
Location l = new Location();
l.setDescription("at home");
em.persist(l);
int id = l.getId();
the getID method allways returns a null object. The row is added in the DB, but the auto incremented ID is not returned to the entity bean!
I know I could solve this by generating the ID's myself, but one of the strengths of autoincrement should be not to have to do this, no?
If anyone has a clue how to solve this issue, I would very much appreciate it !
Michiel
Edited by: Michiel82 on Dec 6, 2007 6:01 AM

Answer 1

No reactions so far ... this is a work-around for the issue :
I've created an additional table sequence with two fields: gen_key and gen_value. Then, in my Location entity bean I can add the following:
@TableGenerator(
name="locationGen",
table="sequence",
pkColumnName="gen_key",
valueColumnName="gen_value",
pkColumnValue="location",
allocationSize=1
@Id
@GeneratedValue(strategy=GenerationType.TABLE,generator="locationGen")
@Column(name = "id", nullable=false)
private Short id;
This generates the primary key in the bussiness logic, but I would like to get the autogenerated key from my MySQL database (see previous post). Is this perhaps not supported by EJB3.0?
Michiel