DSE Graph with Java Driver, how to add edges - cassandra

Question

I want to build a graph completely with the Datastax Java Driver. I managed to insert vertices, but I have no clue how to add edges to existing vertices.
When I run the following code
session.executeGraph("parent = g.V().has('businessId','sys-1').next()");
session.executeGraph("child = g.V().has('businessId','sys-2').next()");
session.executeGraph("parent.addEdge('consistsOf', child)");
I get an exception
Exception in thread "main" com.datastax.driver.core.exceptions.InvalidQueryException: No such property: parent for class: Script285
at com.datastax.driver.core.exceptions.InvalidQueryException.copy(InvalidQueryException.java:50)
at com.datastax.driver.dse.DriverThrowables.propagateCause(DriverThrowables.java:29)
at com.datastax.driver.dse.DefaultDseSession.executeGraph(DefaultDseSession.java:77)
at com.datastax.driver.dse.DefaultDseSession.executeGraph(DefaultDseSession.java:64)
at de.pratho.valpro.tools.Main.main(Main.java:41)
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:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: com.datastax.driver.core.exceptions.InvalidQueryException: No such property: parent for class: Script285
at com.datastax.driver.core.Responses$Error.asException(Responses.java:136)
at com.datastax.driver.core.DefaultResultSetFuture.onSet(DefaultResultSetFuture.java:179)
at com.datastax.driver.core.RequestHandler.setFinalResult(RequestHandler.java:173)
at com.datastax.driver.core.RequestHandler.access$2500(RequestHandler.java:43)
at com.datastax.driver.core.RequestHandler$SpeculativeExecution.setFinalResult(RequestHandler.java:788)
at com.datastax.driver.core.RequestHandler$SpeculativeExecution.onSet(RequestHandler.java:607)
at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:1012)
at com.datastax.driver.core.Connection$Dispatcher.channelRead0(Connection.java:935)
at io.netty.channel.SimpleChannelInboundHandler.channelRead(SimpleChannelInboundHandler.java:105)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:266)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:276)
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:263)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:318)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:304)
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:846)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:511)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:468)
at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:382)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:354)
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:112)
at java.lang.Thread.run(Thread.java:745)
When I run the gremlin statements in the gremlin_console_window it is working fine. So I think variables like parent and child are not working within a Java DseSession?
Unfortunately, I was not able to find much information about how to work with the Java Driver properly.

Answer 1

It looks like you have to create it within the context of the same script, i.e:
DseCluster dseCluster = DseCluster.builder()
.addContactPoint("127.0.0.1")
.withGraphOptions(new GraphOptions().setGraphName("demo"))
.build();
DseSession dseSession = dseCluster.newSession();
SimpleGraphStatement s = new SimpleGraphStatement(
"def v1 = g.V(id1).next()\n" +
"def v2 = g.V(id2).next()\n" +
"v1.addEdge('relates', v2)");
dseSession.executeGraph(s);
I think the reason for this is that these commands are just interpreted as independent gremlin queries.
I believe this set of documentation may be helpful to you.