例外：查询结果集不可修改 我在这里看到了类似的问题，但它没有回答我的问题，所以我决定开始一个新的。
我正在尝试通过临时存储 Google App Engine 的 High Replication 数据存储来解决读取不一致的问题 ( https://groups.google.com/forum/?fromgroups=#!topic/google-appengine/E95wH0RkJUE )静态变量中最后添加的对象。
每当用户添加一个新航班时，它不会直接保存新航班对象，而是将其作为静态变量存储在 PMF 中。
因此，当在查询中获取航班列表时，它将结果存储在列表中，并将列表与最后添加的对象进行比较，如果最后添加的对象不在列表中，我手动将最后添加的对象添加到名单。
但是，使用此方法，每当列表中缺少新添加的对象并且我手动添加它时，我都会收到以下异常。
Oct 6, 2012 2:19:38 PM com.google.apphosting.utils.jetty.JettyLogger warn
WARNING: /
java.lang.UnsupportedOperationException: Query result sets are not modifiable
at org.datanucleus.store.query.AbstractQueryResult.add(AbstractQueryResult.java:222)
at com.jimfoo88.helloorm.GetFlights.queryJDO(GetFlights.java:101)
at com.jimfoo88.helloorm.GetFlights.doGet(GetFlights.java:50)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
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$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60)
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$ApiProxyHandler.handle(JettyContainerService.java:370)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
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)
我下面的代码基于谷歌应用引擎示例 HelloORM http://code.google.com/p/datanucleus-appengine/source/browse/trunk/demos/helloorm/src/com/google/appengine/demos/helloorm /GetFlights.java?r=736
我只展示我为简化阅读而修改的部分。
AddFlight.java
private void doPostJDO(Flight f) {
PersistenceManager pm = PMF.get().getPersistenceManager();
PMF.setLastObjectAdded(f);
try {
pm.makePersistent(f);
} finally {
pm.close();
}
}
PMF.java
// Copyright 2008 Google Inc. All Rights Reserved.
package com.jimfoo88.helloorm;
import javax.jdo.JDOHelper;
import javax.jdo.PersistenceManagerFactory;
/**
* @author Max Ross <maxr@google.com>
*/
public final class PMF {
private static Object lastObjectAdded;
private static final PersistenceManagerFactory INSTANCE = JDOHelper.getPersistenceManagerFactory("transactions-optional");
public static Object getLastObjectAdded() {
return lastObjectAdded;
}
public static void setLastObjectAdded(Object lastObject) {
lastObjectAdded = lastObject;
}
public static PersistenceManagerFactory get() {
return INSTANCE;
}
private PMF() {}
}
GetFlights.java
private Collection<Flight> queryJDO(String query) {
PersistenceManager pm = PMF.get().getPersistenceManager();
try {
List<Flight> flights = (List<Flight>) pm.newQuery(query).execute();
// Force all results to be pulled back before we close the entity
// manager.
// We could have also called pm.detachCopyAll()
flights.size();
//pm.detachCopyAll(flights);
boolean found = false;
try {
for (Flight f : flights) {
if ((Flight) PMF.getLastObjectAdded() == null) {
found = true;
break;
}
if (f.getDest() == ((Flight) PMF.getLastObjectAdded())
.getDest()
&& f.getOrig() == ((Flight) PMF
.getLastObjectAdded()).getOrig()) {
logger.info("found object " + f.toString()
+ "in datastore");
found = true;
break;
}
}
if (found == false) {
logger.info("did not find object "
+ (Flight) PMF.getLastObjectAdded()
+ " in datastore, need to add it");
flights.add((Flight) PMF.getLastObjectAdded());
}
} catch (NullPointerException e) {
logger.error(e.getMessage());
}
return flights;
} finally {
pm.close();
}
}
如果有人能指出我的错误，将不胜感激。如果有任何更好的方法来解决这个问题，请告诉我。谢谢。