Cannot persist a GameData object

[Matt Giuca]

I am having trouble creating GameData objects and persisting them in the database. I created a GameData object like this (in DataTestServiceImpl.populateDatastore):

      GameData[] games = new GameData[] {
                                        new GameData("test", devteams[0])
                                      };
      pm.makePersistentAll(games);

Then, clicking the Populate button results in this error at runtime:

> The owner field game of element class
> au.edu.unimelb.csse.mugle.server.model.AchievementData
> has an incorrect type "au.edu.unimelb.csse.mugle.shared.model.Game". Should
> be "au.edu.unimelb.csse.mugle.server.model.GameData"

That is on the line:
    pm.makePersistentAll(games);

I assume this is because we have a class GameData which has a Set<AchievementData> mappedBy "game", but the AchievementData's game field has type Game. I believe that AchievementData's game field should have type GameData. Am I correct?

I replaced all uses of the Game type in AchievementData with GameData. This fixes that error, but now it generates another exception on the same line:

> Class "au.edu.unimelb.csse.mugle.server.model.GameData" has collection
> field "achievements" and this has no mapping in the table for the element
> class "au.edu.unimelb.csse.mugle.server.model.AchievementData" owner
> field "game"

I can't figure this one out. The GameData.achievements field has type Set<AchievementData> mappedBy "game", and the AchievementData.game field has type GameData. This seems to be the normal way of doing things in https://code.google.com/appengine/docs/java/datastore/jdo/relationships.html, so why is it giving this error?

[Matt Giuca (mgiuca)]

I have fixed the first exception (Game -> GameData) in trunk r115. Now stuck on the second one.

[Scott Ritchie (sritchie)]

Im not getting this error yet - its currently failing at making the DevTeam Persistent:

00:08:08.757 [ERROR] javax.servlet.ServletContext log: Exception while dispatching incoming RPC call com.google.gwt.user.server.rpc.UnexpectedException: Service method 'public abstract java.lang.String au.edu.unimelb.csse.mugle.client.DataTestService.populateDatastore()' threw an unexpected exception: org.datanucleus.exceptions.NucleusException: App Engine ORM does not support multiple parent key provider fields.
......
at au.edu.unimelb.csse.mugle.server.DataTestServiceImpl.populateDatastore(DataTestServiceImpl.java:61)

I've done a quick search and come up with:
As the exception states, on App Engine an Entity cannot have multiple parents. This
is because OneToMany is tied to the concept of ancestor in the datastore. Each
entity can only have one direct ancestor.

I'll see what can be done, but i think what will end up happening is i'll have to change all the relations in the code to be unowned, so that theyre sets of keys with no mappings.
This will also fix the issue with the Game mapping.

[Scott Ritchie (sritchie)]

I've updated the ER Diagram in revision 118 to reflect the changes i plan to implement. Let me know if you disagree with which relation I've designated as owned or unowned in the updated diagram

[Matt Giuca (mgiuca)]

Well I'm getting an exception persisting the DevTeam as well, but only the first time. If you click again, it should work.

But yeah, okay. If unowned works, let's go with that. It seems like the difference between owned vs unowned is that owned is better for type safety, but unowned works more often. Seems like an annoying distinction (I like things with type safety that work), but given the choice, go with unowned.

That just means replacing all of the actual object types with 'Key', right?

[Scott Ritchie (sritchie)]

Making them all unowned has worked, need to make sure all the getters and setters are correct now that we're managing our own relations and will commit a fix

[Scott Ritchie (sritchie)]

Fixed in revision 119,
But new bugs #744035 and #774929 have been raised.