我正在使用JDO在Google App Engine中创建一个Web应用程序，并得到一个JDOFatalUserException：
javax.jdo.JDOFatalUserException: Detected attempt to establish User(15) as the
parent of SessionToken("VALID_USER_TOKEN") but the entity identified
by SessionToken("VALID_USER_TOKEN") has already been persisted
without a parent. A parent cannot be established or changed once an
object has been persisted.
我有User类，其中有一个SessionToken。我想在数据存储区中同时存储User和SessionToken。用户密钥是自动生成的，而SessionToken密钥是由我生成的。
@PersistenceCapable
public class User {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;
@Persistent
private SessionToken sessionToken;
//getters and setters...
}
和：
@PersistenceCapable
public class SessionToken {
@PrimaryKey
private Key token;
public SessionToken(Key token) {
this.token = token;
}
//getters and setters...
}
然后，我想创建一个用户，所以我这样做：
PersistenceManager pm = PMF.get().getPersistenceManager();
User user = new User();
Key key = KeyFactory.createKey(SessionToken.class.getSimpleName(),
"VALID_USER_TOKEN");
user.setSessionToken(new SessionToken(key));
try {
pm.makePersistent(user);
} finally {
pm.close();
}
这是完整的异常转储：
javax.jdo.JDOFatalUserException: Detected attempt to establish User(15) as the parent of SessionToken("VALID_USER_TOKEN") but the entity identified by SessionToken("VALID_USER_TOKEN") has already been persisted without a parent. A parent cannot be established or changed once an object has been persisted.
at org.datanucleus.api.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:498)
at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:736)
at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:756)
at com.mockgaeapp.UsersEndpoint.register(UsersEndpoint.java:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:115)
at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:239)
at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:161)
at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:120)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61)
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:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
at org.mortbay.jetty.servlet.ServletHandler$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.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:409)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$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)
我不明白该错误，因为在保存用户之前我不保存SessionToken对象。
此异常是什么意思？
最佳答案
您的代码告诉JDO在User和SessionToken对象之间具有“拥有”关系，在这种情况下，子实体应该以父项的键作为其父项（在数据存储区中），而您明确设置了键值而没有父项。
请尝试使用'unowned' relationship。