Sharing sequences between 2 entities

tonioc · **Posted:** Thu Jan 11, 2007 7:49 pm

[b]Hibernate version:3,2,1,GA

I'm trying to share a sequence between two tables, as EJB3.0 persistence api docs states:

Quote:

This annotation defines a primary key generator that may be referenced by name when a generator element is specified for the GeneratedValue annotation. A sequence generator may be specified on the entity class or on the primary key field or property. The scope of the generator name is global to the persistence unit (across all generator types).

My First Entity has the following anotations

Code:

@Id
@Column(name = "id", unique = true, nullable = false, insertable = false, updatable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="services_process_seq")
@SequenceGenerator(name="services_process_seq", sequenceName="services_process_id_seq")
private int id;

In My Second Entity I tried:

Code:

@Id
@Column(name = "id", unique = true, nullable = false, insertable = false, updatable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="services_process_seq")
private int id;

Id doesn't work it gives:

Code:

Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.AnnotationException: Unknown Id.generator: services_process_seq

Then I tried

Code:

@Id
@Column(name = "id", unique = true, nullable = false, insertable = false, updatable = false)
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="services_process_seq")
@SequenceGenerator(name="services_process_seq")
private int id;

It gives me this error,(because hibernate_sequence does no exist, of course this is correct I'm expecting to use serices_process_id_seq)

Code:

   select
        nextval ('hibernate_sequence')
ERROR: Could not create data: org.hibernate.exception.SQLGrammarException: could not get next sequence value

I've tried some more variants as writing de @SequenceGenerator at class level, not field/attribute, etc..., and all of them give me the same error.

Can anyone tell me if I'm expecting something that won't happen, I'm writing something wrong ?

Any help will be welcomed
Thanks in advance
tonio

emmanuel · **Posted:** Fri Jan 12, 2007 8:06 pm

services_process_id_seq != services_process_seq

tonioc · **Posted:** Mon Jan 15, 2007 3:18 pm

Thanks Emanuell,

But this did not resolve the issue, all works the same way as I described in my first e-mail changing the name of both @GeneratedValue's generator attribute and @SequenceGenerator's name attribute to "services_process_id_seq".

Just to make sure that you understand what I need:

If I use the same code for both classes it will work but they are not sharing the generator for example:

Code:

   @Id
   @Column(name = "id", unique = true, nullable = false, insertable = true, updatable = false)
   @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="services_process_id_seq")
   @SequenceGenerator(name="services_process_id_seq", sequenceName="services_process_id_seq")
   public int getId() {
      return this.id;
   }

What will happen is:

Insert in class1
id=51

insert in class2
id=101

new insert in class1
id=52

What I expect to happen is
Insert in class1
id=51

insert in class2
id=52

new insert in class1
id=53

Hope I'm clear enough
Thanks again

vinodhts · **Posted:** Tue Jan 16, 2007 11:07 am

Try using/setting the increment value to be 1 or try using hilo generator .Here you need to create a table named hi_value.

<id name="losItmId" type="int">
<generator class="hilo">
<param name="table">hi_value</param>
<param name="column">next_value</param>
<param name="max_lo">1</param>
</generator>
</id>

Thanks,
Vinodh

andydale · **Posted:** Tue Jan 16, 2007 11:33 am

Hi,

Try adding the follwing items

Code:

initialValue = 1, allocationSize = 1

In your @SequenceGenerator annotation

Andy

tonioc · **Posted:** Tue Jan 16, 2007 1:11 pm

Thanks all,

Yes, yes I forgot to mention, I new that changing allocationSize to 1 will solve my problem, but this implies making two calls to the database for every insert in this tables.

Now as de api documentation says, an this is the precise question:

Must we be able to share a sequence between two entities or not, I'm misunderstanding the documentation or is this a feature jboss EJB3.0 persistence is not implementing correctly ?

Thanks again, and I'm stuck to allocationSize=1 until I have some news
tonio

emmanuel · **Posted:** Sun Jan 21, 2007 7:28 pm

ah, the same sequence is shared, not the same generator,
you could try and implement your own identitygenerator to achieve what you want, but you'll have to rely on some static variable somewhere

motte79 · **Joined:** Tue Jul 03, 2007 5:06 am **Posts:** 1

Code:

@emmanuel
ah, the same sequence is shared, not the same generator, 

what's the difference between a shared sequence and a shared generator ?

The SequenceGenerator - Annotation maps a 'name' to a 'sequenceName' - this is a 1:1 relation - therefore if the sequencegenerator is shared the db-sequence has to be shared too ...
http://java.sun.com/javaee/5/docs/api/j ... rator.html

Did i misunderstood the api - doc ?

emmanuel · **Posted:** Tue Jul 03, 2007 11:15 am

For someone not writing a generator strategy there is no difference
For someone write an id generator strategy, it means that several instances of the same generator and for the same set of parameters can exist.