我在Java中为ArangoDB执行AQL查询，以获得特定节点后代的总数。这是代码。
String nodeUserid = nodeuserid.getText().trim();
Map<String, Object> bindVars = new MapBuilder().put("nodeid", nodeUserid).get();
CursorResult cs = arangoDriver.executeAqlQuery("LET x = (FOR v IN 1..1000 OUTBOUND @nodeid GRAPH 'TempPeoplesApp' "
+ " RETURN v.x)"
+ " RETURN SUM(x)", bindVars, null,null);
int count = cs.getCount();
但是在运行时它会给出一个例外情况，
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1768)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1651)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Node.fireEvent(Node.java:8175)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:204)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3746)
at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
at com.sun.glass.ui.View.notifyMouse(View.java:898)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1765)
... 47 more
Caused by: java.lang.NullPointerException
at java.lang.Class.isAssignableFrom(Native Method)
at com.arangodb.entity.EntityDeserializers$CursorEntityDeserializer.getResultObjects(EntityDeserializers.java:686)
at com.arangodb.entity.EntityDeserializers$CursorEntityDeserializer.deserialize(EntityDeserializers.java:647)
at com.arangodb.entity.EntityDeserializers$CursorEntityDeserializer.deserialize(EntityDeserializers.java:621)
at com.google.gson.TreeTypeAdapter.read(TreeTypeAdapter.java:58)
at com.google.gson.Gson.fromJson(Gson.java:861)
at com.google.gson.Gson.fromJson(Gson.java:826)
at com.google.gson.Gson.fromJson(Gson.java:775)
at com.arangodb.entity.EntityFactory.createEntity(EntityFactory.java:163)
at com.arangodb.BaseArangoDriver.createEntityImpl(BaseArangoDriver.java:367)
at com.arangodb.BaseArangoDriver.createEntityWithFallback(BaseArangoDriver.java:259)
at com.arangodb.BaseArangoDriver.createEntity(BaseArangoDriver.java:236)
at com.arangodb.BaseArangoDriver.createEntity(BaseArangoDriver.java:311)
at com.arangodb.impl.InternalCursorDriverImpl.executeCursorEntityQuery(InternalCursorDriverImpl.java:81)
at com.arangodb.impl.InternalCursorDriverImpl.executeAqlQuery(InternalCursorDriverImpl.java:148)
at com.arangodb.ArangoDriver.executeAqlQuery(ArangoDriver.java:2144)
at peoplesapptree.TreeCreationController.displayDescendents(TreeCreationController.java:169)
... 57 more
执行arangoDriver.executeAqlQuery方法时会出现异常。那么这个查询有什么不对吗？谁有人建议？我是ArangoDB的新手
谢谢， Mayank
答案 0 :(得分：2)
您使用的是哪个版本的ArangoDB和ArangoDB-Java-Driver？
方法executeAqlQuery需要知道您期望的CursorResult中的哪种类型。它是最后一个参数。在您的情况下，您可能希望在Aql中使用整数作为总和。
String nodeUserid = nodeuserid.getText().trim();
Map<String, Object> bindVars = new MapBuilder().put("nodeid", nodeUserid).get();
CursorResult<Integer> cs = arangoDriver.executeAqlQuery(
"LET x = (FOR v IN 1..1000 OUTBOUND @nodeid GRAPH 'TempPeoplesApp' " + " RETURN v.x)" + " RETURN SUM(x)",
bindVars, null, Integer.class);
Integer sum = cs.getUniqueResult();
getCount()返回结果总数。 getFullCount()返回带有（aql）限制子句的结果总数。在您的情况下，您的aql仅返回1个结果，即总和。 aql可以返回结果列表。当您只有1个结果时，可以使用getUniqueResult获得结果，当您有n个结果时，请使用方法iterator()或asList()并迭代它。
方法executeAqlQuery支持所有原始类型，Map，List和uniqe aql结果Java-Beans的包装类。