问题
Apologies as this might be very basic question on the topic but I am new to Gremlin/DSE Graph and i tried many ways to extract data i am inserting to my graph but somehow i am unable to make it work.
Here is what i have: 1. Graph with allow_scans set to true 2. Schema with propertyKey and vertexes defined and materialized index on NodeID of all Vertexes.
There are no relationships right now, just vertexes with data points.
I wrote a program to insert all my nodes to DSE Graph which is working successfully as i get response like below after program created every Vertex:
Result({u'id': {u'out_vertex': {u'community_id': 853347840, u'~label': u'vertex', u'member_id': 14}, u'~type': u'Name', u'local_id': u'00000000-0000-8012-0000-000000000000'}, u'value': u'amount', u'label': u'Name'})]
Ok So now the nodes are inserted, i want to extract them and print their names: So i did:
g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').values('Name');
Above failed successfully with blank result. I mean it runs successfully with null output like there is no error but then there is no output. (null in gremlin-console and 'Success - No Results' in DataStax Studio)
Then i came across documentation that graph will not know if the 'has' will only return one node or more, so i used next for iterating as per documentation and tutorials:
g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').next().values('Name');
Even this failed with
org.apache.tinkerpop.gremlin.driver.exception.ResponseException
(Datastax studio doesnt show more information) - How can i debug this further?
I even came across lambda approach in which i use map :
g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').map{it.get().value('Name')};
which responded with 'it' not being defined.
(i even tried valueMap - not sure if it was even required)
What am i doing wrong to find and print properties values of a node?
Any directions or query which can help me extract the names and other properties? Even a multi-step query? however i don't think this should be that complicated.
UPDATE:
As per answer i get the following traceback:
gremlin> :> g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').valueMap(true).next();
org.apache.tinkerpop.gremlin.groovy.plugin.RemoteException
Type ':help' or ':h' for help.
Display stack trace? [yN]y
org.apache.tinkerpop.gremlin.groovy.plugin.RemoteException
at org.apache.tinkerpop.gremlin.console.groovy.plugin.DriverRemoteAcceptor.submit(DriverRemoteAcceptor.java:170)
at org.apache.tinkerpop.gremlin.console.commands.SubmitCommand.execute(SubmitCommand.groovy:41)
at org.codehaus.groovy.tools.shell.Shell.execute(Shell.groovy:104)
at org.codehaus.groovy.tools.shell.Groovysh.super$2$execute(Groovysh.groovy)
at sun.reflect.GeneratedMethodAccessor15.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.codehaus.groovy.tools.shell.Groovysh.executeCommand(Groovysh.groovy:259)
at org.apache.tinkerpop.gremlin.console.GremlinGroovysh.execute(GremlinGroovysh.groovy:84)
at org.codehaus.groovy.tools.shell.Shell.leftShift(Shell.groovy:122)
at org.codehaus.groovy.tools.shell.ShellRunner.work(ShellRunner.groovy:95)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$work(InteractiveShellRunner.groovy)
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:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:152)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.work(InteractiveShellRunner.groovy:124)
at org.codehaus.groovy.tools.shell.ShellRunner.run(ShellRunner.groovy:59)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$run(InteractiveShellRunner.groovy)
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:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1215)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:132)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:152)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.run(InteractiveShellRunner.groovy:83)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:232)
at org.apache.tinkerpop.gremlin.console.Console.<init>(Console.groovy:152)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:232)
at org.apache.tinkerpop.gremlin.console.Console.main(Console.groovy:401)
I am able to do some similar operations in another graph. Is something wrong with the graph?
UPDATE 2
My Graph vertices were wrongly defined.
The key to drill down to this solution is in the ~label in the result. It points to vertex instead it should be Field
While defining the data insert team had put label in quotes when they had to put mention label without quotes. Hence i was not able to traverse the nodes.
回答1:
You need to make sure to iterate the traversal. Most commonly you would use either:
iterate()get zero resultnext()get one resulttoList()get many results
I'd guess that NodeID is unique, so try something like this:
g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').
values('Name').next();
If you're interested in all of the properties on that vertex, try:
g.V().hasLabel('FIELD').has('NodeID','2559b635f077e86c7370ab1c4c798a06').
valueMap(true).next();
来源：https://stackoverflow.com/questions/43283837/unable-to-print-node-properties-in-dse-graph