如何计算距离为 k 的顶点数？

Question

例如，我想获取距离为 2（精确）的所有顶点，例如：

V1 <--> V2 <--> V3

我想为我的 V1 获取所有 V3。

这可以通过这样的查询方式完成：

select both().both().both.size() from <RID>

但我的问题是：如何使用 TinkerPop 从 Java API 执行此操作，而不直接使用 sql 查询进行查询，而是使用 TinkerPop 遍历方法。

P.S.：对不起我的英语不好。

---

更新：

试过了：

OrientGraph 图 = new OrientGraph(Network.factory.acquire());

    try {
        GremlinPipeline<Vertex, Long> pipe = new GremlinPipeline();
        Long count = (pipe.start(graph.getVertex("#12:1")).both()).both().count();
        System.out.println(count);
    } catch(Exception e) {
        e.printStackTrace();
        graph.rollback();
    } finally {
        graph.shutdown();
    }

堆栈跟踪是：

 java.lang.NullPointerException
at com.tinkerpop.blueprints.impls.orient.OrientElement.getRecord(OrientElement.java:326)
at com.tinkerpop.blueprints.impls.orient.OrientVertex.getEdges(OrientVertex.java:798)
at com.tinkerpop.blueprints.impls.orient.OrientVertex.getEdges(OrientVertex.java:780)
at com.tinkerpop.blueprints.util.DefaultVertexQuery$DefaultVertexQueryIterable.<init>(DefaultVertexQuery.java:110)
at com.tinkerpop.blueprints.util.DefaultVertexQuery.vertices(DefaultVertexQuery.java:84)
at com.tinkerpop.pipes.transform.VertexQueryPipe.processNextStart(VertexQueryPipe.java:113)
at com.tinkerpop.pipes.transform.VertexQueryPipe.processNextStart(VertexQueryPipe.java:19)
at com.tinkerpop.pipes.AbstractPipe.next(AbstractPipe.java:89)
at com.tinkerpop.pipes.util.Pipeline.next(Pipeline.java:115)
at com.tinkerpop.pipes.util.PipeHelper.counter(PipeHelper.java:107)
at com.tinkerpop.gremlin.java.GremlinPipeline.count(GremlinPipeline.java:1534)
at models.service.NetworkFacadeREST.test(NetworkFacadeREST.java:150)
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 org.glassfish.ejb.security.application.EJBSecurityManager.runMethod(EJBSecurityManager.java:1081)
at org.glassfish.ejb.security.application.EJBSecurityManager.invoke(EJBSecurityManager.java:1153)
at com.sun.ejb.containers.BaseContainer.invokeBeanMethod(BaseContainer.java:4786)
at com.sun.ejb.EjbInvocation.invokeBeanMethod(EjbInvocation.java:656)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:46)
at org.jboss.weld.ejb.SessionBeanInterceptor.aroundInvoke(SessionBeanInterceptor.java:52)
at sun.reflect.GeneratedMethodAccessor99.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.EjbInvocation.proceed(EjbInvocation.java:608)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.doCall(SystemInterceptorProxy.java:163)
at com.sun.ejb.containers.interceptors.SystemInterceptorProxy.aroundInvoke(SystemInterceptorProxy.java:140)
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 com.sun.ejb.containers.interceptors.AroundInvokeInterceptor.intercept(InterceptorManager.java:883)
at com.sun.ejb.containers.interceptors.AroundInvokeChainImpl.invokeNext(InterceptorManager.java:822)
at com.sun.ejb.containers.interceptors.InterceptorManager.intercept(InterceptorManager.java:369)
at com.sun.ejb.containers.BaseContainer.__intercept(BaseContainer.java:4758)
at com.sun.ejb.containers.BaseContainer.intercept(BaseContainer.java:4746)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:88)
at com.sun.proxy.$Proxy305.test(Unknown Source)
at models.service.__EJB31_Generated__NetworkFacadeREST__Intf____Bean__.test(Unknown Source)
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 org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:151)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:171)
at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:195)
at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:104)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:387)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:331)
at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:103)
at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:271)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:297)
at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:254)
at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1028)
at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:372)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:381)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:344)
at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:221)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
a
Severe:   t org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
    at java.lang.Thread.run(Thread.java:745)

我尝试寻找 1 级的朋友，并且成功了。但是当我尝试 both().both() 时，它给了我空指针异常。

我还是个菜鸟，我不知道为什么会这样。谢谢。

---

更新：

试过：Long count = pipe.start(graph.getVertex("#12:1")).both("Worked").has("recommendation","recommended").count(); 和同样的错误；我尝试执行的任何 2 个操作都会引发此错误。

---

更新：

我做了更多的测试，比如跑步：

pipe.start(graph.getVertex(1)).out();
pipe.start(graph.getVertex(1)).both().both();

那些将成功运行，但如果我尝试迭代上述相同的错误将被调用。

pipe.next();
for (Object x : pipe) {}

但如果我迭代成单个对象，它就可以工作，例如：

pipe.start(graph.getVertex(1)).getProperty("X");
pipe.next();

除此之外，.count() 之类的方法会抛出相同的堆栈跟踪。

希望有人能让我了解 Gremlin 的工作原理，看来我无法处理。 （阅读他们的文档）

Answer 1

也许使用 Gremlin：

        OrientGraph graph = new OrientGraph(URL, USER, PW);
        try {

            GremlinPipeline<Vertex, Long> pipe = new GremlinPipeline();
            Long count = pipe.start(graph.getVertex("#11:0")).both().both().count();

        } finally {
            graph.shutdown();
        }