[appengine-java] Re: Unowned relations JPA examples for datanucleus plugin v2

[Marrrck]

Thanks datanucleus!

I thought about the @Unowned annotation but I didn't have the
datanucleus-appengine-2.0.0-RC2.jar in my eclipse build path...

Unfortunately I'm not out of the woods yet. I downloaded and built the
jars from the the svn trunk, and I modified my entities to match
exactly the mapping defined in the JPAManyToManyTest.java from the
unit tests in that project, but when I run my application locally via
eclipse, I get this exception:

Caused by: com.google.appengine.datanucleus.EntityUtils
$ChildWithoutParentException: Detected attempt to establish This(2) as
the parent of That(3) but the entity identified by That(3) has already
been persisted without a parent.  A parent cannot be established or
changed once an object has been persisted.
at
com.google.appengine.datanucleus.EntityUtils.checkParentage(EntityUtils.java:
577)
at
com.google.appengine.datanucleus.scostore.FKSetStore.add(FKSetStore.java:
171)
at org.datanucleus.store.types.sco.backed.Set.add(Set.java:562)


Seems like at runtime the @Unowned is being ignored? Not sure if this
is a classpath issue or maybe something to do with running it locally
in Eclipse using the GAE plugin? I'm not really sure what else to look
for at this point so if you have any ideas for anything else I can
check I'd really appreciate it.


THanks again for the response...

On Jan 22, 11:11 am, datanucleus andy_jeffer...@yahoo.com wrote:
 To make a relation unowned (in v2) you mark (both sides if
 bidirectional) as @Unowned
 Unowned M-N work fine with SVN trunk code, though there may have been
 some things incomplete in RC versions

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[appengine-java] Unowned relations JPA examples for datanucleus plugin v2

[Marrrck]

 Hi Everyone,


I'm trying to get a many-to-many unowned relationship modeled using JPA and 
the appengine-datanucleus v2 plugin, but I can't get it work and all the 
examples I've found online are for JDO or else pre v2 of the plugin. Has 
anyone gotten manytomany or really any kind of unowned relationships to 
work using JPA and v2 of the datanucleus plugin? What would they look like? 
Here's the example I tried:

@Entity
public class This implements Serializable {
 
@Id

@GeneratedValue(strategy = GenerationType.IDENTITY) 

private Key key;

@ManyToMany

private SetThat someOfThat;

}

@Entity

public class That implements Serializable {

  @Id

  private String urlForThat;

}

If I create an instance of That, persist it, and then add it to 
this.getSomeOfThat().add(that); it throws 


Caused by: java.lang.IllegalArgumentException: Cannot parse: 
 http://somesite.org/wiki/index.php?title=Special:Recentchanges===
 at com.google.appengine.api.datastore.KeyFactory.stringToKey(
 KeyFactory.java:192)


Where that string is what I set as the id for That. The fact that it is 
using stringToKey makes me think that it is treating the urlForThat as an 
encoded string key instead of an un-encoded one, which would be what it 
would need if the relationship was owned I think?

The code that does this is something like this:
This this = em.find//get existing instance from entity manager
That t = new That();
t.setUrlForThat(http://somesite.org/wiki/index.php?title=Special:Recentchanges;);
em.persist(t);
this.getSomeOfThat().add(t);

The exception gets thrown at the last line there.

Any idea what I am doing wrong? Or is this just not possible? 

Thanks for the help!

Marc

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