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get sequence number through Eclipselink [message #998157]

Wed, 09 January 2013 13:09

Jorg Heymans

Messages: 26
Registered: July 2009
Location: Belgium

Junior Member

Hi,

I have read the wiki so i know that for getting a sequence value i should be able to do this

long id = em.unwrap(Session.class).getNextSequenceNumberValue(Employee.class).longValue();

However when i try this i get a NPE

Caused by: java.lang.NullPointerException: null
        at org.eclipse.persistence.internal.sequencing.SequencingManager.getNextValue(SequencingManager.java:1067) ~[eclipselink-2.4.1.jar:2.4.1.v20121003-ad44345]
        at org.eclipse.persistence.internal.sequencing.SequencingManager.getNextValue(SequencingManager.java:266) ~[eclipselink-2.4.1.jar:2.4.1.v20121003-ad44345]
        at org.eclipse.persistence.internal.sessions.AbstractSession.getNextSequenceNumberValue(AbstractSession.java:2457) ~[eclipselink-2.4.1.jar:2.4.1.v20121003-ad44345]

Our sequence is just defined like this

@SequenceGenerator(name = "AppId", sequenceName = "SEQ_APP", allocationSize = 500)

Reason i'm asking is that we have mixed jpa en jdbc inserts and i would like them to pull numbers from the same sequence number pool, otherwise the jdbc inserts will have ids that are 500 apart each time which is not desired.

Any thoughts ?
Jorg

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Re: get sequence number through Eclipselink [message #998362 is a reply to message #998157]

Wed, 09 January 2013 21:34

Chris Delahunt

Messages: 1389
Registered: July 2009

Senior Member

Are you able to insert a new Employee instance using JPA and have the sequence generated? For example em.persist(new Employee());

If not, then I believe you might be missing the @GeneratedValue annotation on the ID that ties the defined SequenceGenerator to the Employee class, and might result in the NPE you see when trying to get it through native API.

Best Regards,
Chris

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Re: get sequence number through Eclipselink [message #998506 is a reply to message #998157]

Thu, 10 January 2013 06:06

Tom Eugelink

Messages: 817
Registered: July 2009

Senior Member

On 2013-01-09 14:09, Jorg Heymans wrote:
> Reason i'm asking is that we have mixed jpa en jdbc inserts and i would like them to pull numbers from the same sequence number pool, otherwise the jdbc inserts will have ids that are 500 apart each time which is not desired.

Not sure why your call is failing, but I do about the same and that works great. So this should work.

Tom

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Re: get sequence number through Eclipselink [message #998559 is a reply to message #998506]

Thu, 10 January 2013 08:35

Jorg Heymans

Messages: 26
Registered: July 2009
Location: Belgium

Junior Member

Yes @GeneratedValue is not present on the @Id because it works fine without. This is our setup:

- the @SequenceGenerator is defined on a @MappedSuperclass that all our entities extend from. So we use one sequence for all entities.

@MappedSuperclass
@SequenceGenerator(name = "AppIdentity", sequenceName = "SEQ_APP", allocationSize = 500)
public abstract class AbstractDatabaseEntity {
}

- each entity extends this mapped superclass and defines its @Id with something like this:

    @Id
    @Column(name = "ID")
    private String id;

Apparently there is no need for @GeneratedValue on each @Id definition, it defaults to the defined sequencegenerator in the base class.

So when i then explicitly add an @GeneratedValue annotation to the entity

    @Id
    @Column(name = "ID")
    @GeneratedValue(generator="AppIdentity")
    private String id;

then the NPE disappears. Is this a bug then ? I can add it everywhere no problem, but perhaps EL should take into account the mappedsuperclass when searching for the sequencegenerator.

Thanks!

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Re: get sequence number through Eclipselink [message #998709 is a reply to message #998559]

Thu, 10 January 2013 14:39

James Sutherland

Messages: 1939
Registered: July 2009
Location: Ottawa, Canada

Senior Member

If you don't use @GeneratedValue, then tere is no generated value, the id will be null, and you cannot get the sequence generator for the class, as it has none.

To generate an id you need to use @GeneratedValue.

James : Wiki : Book : Blog : Twitter

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Re: get sequence number through Eclipselink [message #1004062 is a reply to message #998157]

Tue, 22 January 2013 14:09

GianMaria Romanato

Messages: 72
Registered: July 2009

Member

Hello, I have another question on the same subject.

EclipseLink does support custom sequence generators, as explained here:
http://wiki.eclipse.org/EclipseLink/Examples/JPA/CustomSequencing#Using_the_Sequence

When using a sequence generator that returns a sequence value that is not a number (for example an UUID, or any other string), the above method is not applicable because it forces the returned sequence value to be a subtype of Number.

I found an alternative path:

entityManager.unwrap(org.eclipse.persistence.jpa.JpaEntityManager.class).getServerSession().getSequencing().getNextValue(domainClass);

and it seems to work properly, however it is using the org.eclipse.persistence.internal.sequencing.Sequencing interface which belongs to an internal package. Is there a safer way of obtaining the next sequence value when a custom generator is used and the data type is not a number?

Thanks in advance
Giamma.

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