App Engine's JDO implementation does not support interfaces. For the time
being, you'll have to make BlockModule a concrete @PersistenceCapable class.
Some progress is being made on adding inheritance support as well, so this
will eventually be an option too.
- Jason
On Wed, Oct 7, 2009 at 7:59 AM, Prashant <antsh...@gmail.com> wrote:
> Hi,
>
> I have following object child relationship. All the objects are getting
> saved properly but when I try to fetch child object I am getting
> NullPointerException. This error is not because of lazy loading as I am
> accessing the child before closing the PersistentManager. Aren't interfaces
> fully supported by JOD?
>
>
> ============ Parent Object Class ==============
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class Block implements Serializable {
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> private Long block_id;
>
> @Persistent(defaultFetchGroup = "true")
> private BlockModule block_module;
> ....
> ....
>
>
>
> ============= Child Interface and Implementation ============
> public interface BlockModule extends Serializable{
>
> String getTitle(HttpServletRequest req);
>
> String getContent(HttpServletRequest req);
> }
>
>
>
>
> @PersistenceCapable(identityType = IdentityType.APPLICATION)
> public class BlockTextHTML implements BlockModule{
>
> @PrimaryKey
> @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> protected Key key;
>
> @Persistent
> private String block_title;
>
> @Persistent(types = {BlockTextHTML.class})
> private String block_content;
>
> ....
> ....
>
>
>
> ================= ERROR LOG ================
> Uncaught exception from servlet
> java.lang.NullPointerException
> at
> org.datanucleus.store.mapped.identifier.JPOXIdentifierFactory.newDatastoreContainerIdentifier(JPOXIdentifierFactory.java:258)
> at
> org.datanucleus.store.appengine.DatastoreRelationFieldManager.lookupOneToOneChild(DatastoreRelationFieldManager.java:316)
> at
> org.datanucleus.store.appengine.DatastoreRelationFieldManager.fetchRelationField(DatastoreRelationFieldManager.java:286)
> at
> org.datanucleus.store.appengine.DatastoreFieldManager.fetchObjectField(DatastoreFieldManager.java:271)
> at
> org.datanucleus.state.AbstractStateManager.replacingObjectField(AbstractStateManager.java:1197)
> at antshpra.Block.jdoReplaceField(Block.java)
> at antshpra.Block.jdoReplaceFields(Block.java)
> at
> org.datanucleus.state.JDOStateManagerImpl.replaceFields(JDOStateManagerImpl.java:2772)
> at
> org.datanucleus.state.JDOStateManagerImpl.replaceFields(JDOStateManagerImpl.java:2791)
> at
> org.datanucleus.store.appengine.DatastorePersistenceHandler.fetchObject(DatastorePersistenceHandler.java:443)
> at
> org.datanucleus.state.JDOStateManagerImpl.loadSpecifiedFields(JDOStateManagerImpl.java:1519)
> at
> org.datanucleus.state.JDOStateManagerImpl.isLoaded(JDOStateManagerImpl.java:1925)
> at antshpra.Block.jdoGetModule(Block.java)
> at antshpra.Block.getModule(Block.java:77)
> at antshpra.servlets.InitializeDemo.doRequest(InitializeDemo.java:28)
> at antshpra.Main.doGet(Main.java:76)
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:693)
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
> at
> org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:487)
> at
> org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1093)
> at
> com.google.apphosting.runtime.jetty.SaveSessionFilter.doFilter(SaveSessionFilter.java:35)
> at
> org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
> at
> com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
> at
> org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1084)
> at
> org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:360)
> at
> org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
> at
> org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
> at
> org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712)
> at
> org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
> at
> com.google.apphosting.runtime.jetty.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:237)
> at
> org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
> at org.mortbay.jetty.Server.handle(Server.java:313)
> at
> org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:506)
> at
> org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:830)
> at
> com.google.apphosting.runtime.jetty.RpcRequestParser.parseAvailable(RpcRequestParser.java:76)
> at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
> at
> com.google.apphosting.runtime.jetty.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:139)
> at
> com.google.apphosting.runtime.JavaRuntime.handleRequest(JavaRuntime.java:235)
> at
> com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4950)
> at
> com.google.apphosting.base.RuntimePb$EvaluationRuntime$6.handleBlockingRequest(RuntimePb.java:4948)
> at
> com.google.net.rpc.impl.BlockingApplicationHandler.handleRequest(BlockingApplicationHandler.java:24)
> at
> com.google.net.rpc.impl.RpcUtil.runRpcInApplication(RpcUtil.java:359)
> at com.google.net.rpc.impl.Server$2.run(Server.java:823)
> at
> com.google.tracing.LocalTraceSpanRunnable.run(LocalTraceSpanRunnable.java:56)
> at
> com.google.tracing.LocalTraceSpanBuilder.internalContinueSpan(LocalTraceSpanBuilder.java:516)
> at com.google.net.rpc.impl.Server.startRpc(Server.java:778)
> at com.google.net.rpc.impl.Server.processRequest(Server.java:351)
> at
> com.google.net.rpc.impl.ServerConnection.messageReceived(ServerConnection.java:437)
> at
> com.google.net.rpc.impl.RpcConnection.parseMessages(RpcConnection.java:319)
> at
> com.google.net.rpc.impl.RpcConnection.dataReceived(RpcConnection.java:290)
> at com.google.net.async.Connection.handleReadEvent(Connection.java:428)
> at
> com.google.net.async.EventDispatcher.processNetworkEvents(EventDispatcher.java:762)
> at
> com.google.net.async.EventDispatcher.internalLoop(EventDispatcher.java:207)
> at com.google.net.async.EventDispatcher.loop(EventDispatcher.java:101)
> at
> com.google.net.rpc.RpcService.runUntilServerShutdown(RpcService.java:251)
> at
> com.google.apphosting.runtime.JavaRuntime$RpcRunnable.run(JavaRuntime.java:392)
> at java.lang.Thread.run(Unknown Source)
>
> Unexpected exception from servlet: java.lang.NullPointerException
>
>
>
>
> >
>
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