Gremlin add relationship function is giving exception - gremlin

Question

Please see below code:
peopleObj.forEach( item=>{
let user = item.user;
let event = item.event;
var userNode = g.addV('user');
Object.keys(user).forEach(att=>{
console.log('att: ' + att+", val: "+ user[att]);
userNode.property(att, user[att]);
});
userNode.next();
console.log('created userNode');
eventNode = g.addV('event');
Object.keys(event).forEach(att=>{
console.log('att: ' + att+", val: "+ event[att]);
eventNode.property(att, event[att]);
});
eventNode.next();
console.log('created eventNode');
// const names = await g.V().hasLabel('event').values('name').toList();
// console.log(names);
var u_p = g.V().hasLabel('user').has('name',user.name).next();
var e_p = g.V().hasLabel('event').has('name',event.name).next();
var r1 = g.V(u_p).addE('triggers').to(e_p);
r1.next();
}
when I run it in console, I see below error:
(node:30272) UnhandledPromiseRejectionWarning: Error: Server error: Could not locate method: DefaultGraphTraversal.to([{}]) (599)
at DriverRemoteConnection._handleMessage (/Users/frankhe/projects/aws/sam-app/hello-world/node_modules/gremlin/lib/driver/driver-remote-connection.js:180:9)
I followed the Gremlin V3 doc, why the node can be added, but the edge can not be added here?
Another question is in Gremlin, what is the best approach to check existence before creating? if you look at code, I am just creating event directly, but I need to avoid duplicated events, I tries to use await as indicated in the doc, but there is NO await at all in nodeJS. can anyone tell me the best approach provided by Gremlin?
Thanks in advance.
Answer:
My gremlin nodejs is:
"gremlin": "^3.3.4"
and my gremlin server is
apache-tinkerpop-gremlin-server-3.3.4
The most important problem is no matter how I did, I always meet this error:
Server error: Could not locate method: DefaultGraphTraversal.to([{}])
I changed to asyn way already, but useless. Can anyone show me a working sample for using nodeJS with Gremlin?
Thanks
The simplified version is here:
var g1 = graph.traversal().withRemote(new DriverRemoteConnection('ws://localhost:8182/gremlin'));
var v1 = g1.addV('user').property('name','Frank').next(()=>{
console.log('created1')
var v2 = g1.addV('event').property('name','Event1').next(()=>{
console.log('created2')
g1.V(v1).addE('trigger').to(v2).property('weight',0.75).iterate();
});
});
But in the console. I never saw he log info for created1 at all.
Can you give me a working sample in nodeJS?

Answer 1

You are mixing sync and asynchronous executions in the same code.
Consider that when you use:
userNode.next();
console.log('created userNode');
The message is incorrect. next() returns a Promise that gets resolved asynchronously (see: RemoteConnection Submission).
The correct usage would be:
userNode.next().then(() => console.log('created userNode'));
or, if you are using async functions:
await userNode.next();
console.log('created userNode');

Answer 2

Just removed the .next() and g.V(v1) calls and now the example is working well:
const v1 = await g.addV('person').property('name','marko');
const v2 = await g.addV('person').property('name','stephen');
await v1.addE('knows').to(v2).property('weight',0.75).iterate();
I'm using: gremlin#3.4.1