[appengine-java] java.lang.IllegalArgumentException: can't operate on multiple entity groups in a single transaction

[laurent]

i've searched for this error but don't find what it is.

my code :
                ObjectifyService.register(Lock.class);
                ObjectifyService.register(Connection.class);
                ObjectifyService.register(Assignment.class);

                if (ObjectifyService.begin().query(Connection.class).countAll() 
==
0) {

                        Objectify obj = ObjectifyService.beginTransaction();
                        obj.put(new Connection("DE PESSEMIER", "Johann", 
"projet"));
                        obj.put(new Connection("AUCQUIERE", "Eric", "projet"));

                        obj.put(new Lock(1l));

                        obj.getTxn().commit();
                }

com.google.gwt.user.server.rpc.UnexpectedException: Service method
'public abstract java.util.List
miro.shared.GreetingService.getConnections()' threw an unexpected
exception: java.lang.IllegalArgumentException: can't operate on
multiple entity groups in a single transaction. found both Element {
  type: "Connection"
  id: 5
}
 and Element {
  type: "Connection"
  id: 6
}

        at
com.google.gwt.user.server.rpc.RPC.encodeResponseForFailure(RPC.java:
378)
        at
com.google.gwt.user.server.rpc.RPC.invokeAndEncodeResponse(RPC.java:
581)
        at
com.google.gwt.user.server.rpc.RemoteServiceServlet.processCall(RemoteServiceServlet.java:
188)
        at
com.google.gwt.user.server.rpc.RemoteServiceServlet.processPost(RemoteServiceServlet.java:
224)
        at
com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:
62)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:713)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
        at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:
511)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1166)
        at
com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:
51)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1157)
        at
com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:
43)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1157)
        at
com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:
122)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1157)
        at
org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:
388)
        at
org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:
216)
        at
org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:
182)
        at
org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:
765)
        at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:
418)
        at
com.google.apphosting.utils.jetty.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:
70)
        at
org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:
152)
        at com.google.appengine.tools.development.JettyContainerService
$ApiProxyHandler.handle(JettyContainerService.java:349)
        at
org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:
152)
        at org.mortbay.jetty.Server.handle(Server.java:326)
        at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:
542)
        at org.mortbay.jetty.HttpConnection
$RequestHandler.content(HttpConnection.java:938)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
        at
org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:
409)
        at org.mortbay.thread.QueuedThreadPool
$PoolThread.run(QueuedThreadPool.java:582)

Thanks for your request

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