Neo4j Traversal Framework

Radheshyam Verma

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Jan 25, 2016, 2:31:37 AM1/25/16

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Hi,
I am using traversal framework to traverse graph which returns nodes.
Can we somehow specify a limit on number of nodes which the traversal returns like we do in Query using "LIMIT" and "SKIP".
Thanks.

Mattias Persson

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Jan 27, 2016, 3:54:15 AM1/27/16

to Neo4j

With the traversal framework, the actual work of traversing happens lazily on every call on hasNext/next on the returned Traverser (in the end Iterator<Path>). You can simply stop pulling more paths after a certain number of paths have been extracted.

Radheshyam Verma

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Jan 27, 2016, 7:20:13 AM1/27/16

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Thanks for the reply,

So you mean that for each iteration of following 'FOR' loop, a query is sent to get next node from database if it exists.

and that not all the nodes are returned in one go before 'FOR' loop even starts.

for(Node currentNode : database.traversalDescription()
                .depthFirst()
                .uniqueness(Uniqueness.NODE_GLOBAL)
                .order(BranchOrderingPolicies.PREORDER_BREADTH_FIRST)
                .relationships(<RelationshipType>, Direction.BOTH)
                .evaluator(Evaluators.excludeStartPosition())
                .traverse(node)
                .nodes())
        {

}

Thanks for the response again.

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Mattias Persson

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Jan 27, 2016, 10:51:01 AM1/27/16

to Neo4j Development

You're correct in principle, but it's not a new "query" as such that is sent every time. The traversal state is kept between calls to hasNext/next, but that's just a detail.

--

Mattias Persson

Neo4j Hacker at Neo Technology

Radheshyam Verma

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Mar 14, 2016, 3:32:58 AM3/14/16

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Hi Mattias Persson,

I need help regarding an error I get when I start server. Can you help me find the cause? Here is the stacktrace:-

ERROR [org.neo4j]: Exception when stopping org.neo4j.index.impl.lucene.LuceneDataSource@2aad7c69 org.neo4j.index.impl.lucene.LuceneDataSource.unbindLogicalLog()V

java.lang.NoSuchMethodError: org.neo4j.index.impl.lucene.LuceneDataSource.unbindLogicalLog()V

at org.neo4j.index.impl.lucene.LuceneDataSource.stop(LuceneDataSource.java:343)

at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.stop(LifeSupport.java:527)

at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.shutdown(LifeSupport.java:547)

at org.neo4j.kernel.lifecycle.LifeSupport.remove(LifeSupport.java:339)

at org.neo4j.kernel.impl.transaction.XaDataSourceManager.unregisterDataSource(XaDataSourceManager.java:272)

at org.neo4j.index.lucene.LuceneKernelExtension.stop(LuceneKernelExtension.java:92)

at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.stop(LifeSupport.java:527)

at org.neo4j.kernel.lifecycle.LifeSupport.stop(LifeSupport.java:155)

at org.neo4j.kernel.extension.KernelExtensions.stop(KernelExtensions.java:125)

at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.stop(LifeSupport.java:527)

at org.neo4j.kernel.lifecycle.LifeSupport.stop(LifeSupport.java:155)

at org.neo4j.kernel.lifecycle.LifeSupport.shutdown(LifeSupport.java:185)

at org.neo4j.kernel.InternalAbstractGraphDatabase.shutdown(InternalAbstractGraphDatabase.java:809)

at org.springframework.data.neo4j.support.DelegatingGraphDatabase.shutdown(DelegatingGraphDatabase.java:283)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:606)

at org.springframework.beans.factory.support.DisposableBeanAdapter.invokeCustomDestroyMethod(DisposableBeanAdapter.java:353)

at org.springframework.beans.factory.support.DisposableBeanAdapter.destroy(DisposableBeanAdapter.java:276)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroyBean(DefaultSingletonBeanRegistry.java:578)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingleton(DefaultSingletonBeanRegistry.java:554)

at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingleton(DefaultListableBeanFactory.java:925)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.destroySingletons(DefaultSingletonBeanRegistry.java:523)

at org.springframework.beans.factory.support.DefaultListableBeanFactory.destroySingletons(DefaultListableBeanFactory.java:932)

at org.springframework.context.support.AbstractApplicationContext.destroyBeans(AbstractApplicationContext.java:997)

at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:547)

at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:446)

at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:328)

at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:107)

at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4760)

at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5184)

at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)

at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:724)

at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:700)

at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:714)

at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:919)

at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1704)

at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)

at java.util.concurrent.FutureTask.run(FutureTask.java:262)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

at java.lang.Thread.run(Thread.java:745)

2016-03-14 07:10:41.034+0000 ERROR [org.neo4j]: Exception when stopping org.neo4j.index.lucene.LuceneKernelExtension@7addfa02 Component 'org.neo4j.index.impl.lucene.LuceneDataSource@2aad7c69' failed to stop. Please see attached cause exception.

org.neo4j.kernel.lifecycle.LifecycleException: Component 'org.neo4j.index.impl.lucene.LuceneDataSource@2aad7c69' failed to stop. Please see attached cause exception.

at org.neo4j.kernel.lifecycle.LifeSupport$LifecycleInstance.stop(LifeSupport.java:532)