How essential is 'belongsTo'? (a case of NonUniqueObjectException)

[Iulian Dogariu]

Hello all,

Been playing with Grails for some time now, and so far my experience is
quite positive. Except today I hit a brick wall.

Here's the scenario: There are two domain classes, Camera and
CameraManufacturer. Camera essentially looks like this:

class Camera {
       Long id
       Long version
       /* snip */
       String name
       Boolean alive = false

       /* many-to-one, no belonging specified */
       CameraManufacturer manufacturer
}

ApplicationBootStrap.groovy successfully creates and saves several
Camera objects, all having the same CameraManufacturer.

There is also a job which periodically checks that the cameras are
"alive". It's here that I get:

org.hibernate.NonUniqueObjectException: a different object with the same
identifier value was already associated with the session:
[CameraManufacturer#1]

// grails-app/jobs/CameraCheckerJob.groovy
class CameraCheckerJob {
        def startDelay = 20000
        def timeout = 10000

        def execute() {
            Camera.findAll().each { cam |
                // Ping the cam. Assume ping is successful
                println "Cam ${cam} is alive"
                cam.alive = true;
                cam.save()  // Exception thrown HERE
                            // at the second iteration
            }
            println "Job well done"
        }
}

By poking around, I found that the exception no longer occurs if I add
'def belongsTo = CameraManufacturer' to Camera.

Can anyone shed some light on this, please? Is this expected behaviour,
or might I have run into a bug? I have Java experience, but am pretty
new to Hibernate, and the info about NonUniqueObjectException on the
Hibernate forums is not particularly enlightening.

Thanks!

iulian



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[graemer]

This is a combination of a bug and the correct behavoir believe it or not :-)

The bug is that we are not wrapping an open/close transaction sequence
around the execution of the job. This means that a new session is
being opened multiple times which can cause errors like this.

But, you should have belongsTo on the CameraManufacturer as if you
don't deleting a camera will result in the manufacturer being deleted
too (along with many other cameras) due to the cascading nature of
updates.

On 9/16/06, Iulian Dogariu <[hidden email]> wrote:

> Hello all,
>
> Been playing with Grails for some time now, and so far my experience is
> quite positive. Except today I hit a brick wall.
>
> Here's the scenario: There are two domain classes, Camera and
> CameraManufacturer. Camera essentially looks like this:
>
> class Camera {
>        Long id
>        Long version
>        /* snip */
>        String name
>        Boolean alive = false
>
>        /* many-to-one, no belonging specified */
>        CameraManufacturer manufacturer
> }
>
> ApplicationBootStrap.groovy successfully creates and saves several
> Camera objects, all having the same CameraManufacturer.
>
> There is also a job which periodically checks that the cameras are
> "alive". It's here that I get:
>
> org.hibernate.NonUniqueObjectException: a different object with the same
> identifier value was already associated with the session:
> [CameraManufacturer#1]
>
> // grails-app/jobs/CameraCheckerJob.groovy
> class CameraCheckerJob {
>         def startDelay = 20000
>         def timeout = 10000
>
>         def execute() {
>             Camera.findAll().each { cam |
>                 // Ping the cam. Assume ping is successful
>                 println "Cam ${cam} is alive"
>                 cam.alive = true;
>                 cam.save()  // Exception thrown HERE
>                             // at the second iteration
>             }
>             println "Job well done"
>         }
> }
>
> By poking around, I found that the exception no longer occurs if I add
> 'def belongsTo = CameraManufacturer' to Camera.
>
> Can anyone shed some light on this, please? Is this expected behaviour,
> or might I have run into a bug? I have Java experience, but am pretty
> new to Hibernate, and the info about NonUniqueObjectException on the
> Hibernate forums is not particularly enlightening.
>
> Thanks!
>
> iulian
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe from this list please visit:
>
>     http://xircles.codehaus.org/manage_email
>
>

--
Graeme Rocher
Grails Project Lead
http://grails.org

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